Sarah Salimi

Introduction

As someone who requires a lot of sleep to function, sleep has always been an interesting topic to me. According to experts, getting adequate sleep is essential for health and cognitive functioning. However, not all sleep is created equal. Sometimes I sleep poorly and wake up in a foul mood, and other times I feel rested and elated when I wake up. I wanted to see if there were any patterns to my rest that I could uncover by tracking my sleep behaviors over two weeks. My research questions were as follows:

1. How much do I sleep in a day, and what proportion of my daily sleep is accounted for by naps?
2. Do I get better quality rest on certain days of the week than others?
3. Does my mood tend to improve or worsen when waking up from naps?
4. Do I sleep later on days where I take naps, and do my naps degrade the quality of my bedtime sleep?

Before I continue, a disclaimer: my data collection was not perfect. I could not measure the exact time I fell asleep each night. There is also no truly precise way to measure mood or restfulness. However, I did my best to create an accurate picture of my sleep quality over two weeks by keeping a journal next to my bedside table and recording my mood after each occurrence of sleep within 1 hour of waking.

Data Collection

Between March 24 and April 6, 2025, I recorded the number of hours I slept each day, with each row representing an instance of sleep during the day. Of note, there were 14 days in my dataset but 25 rows. This is because I tended to nap most days in addition to going to sleep at night.

Each day, I catalogued the date, the day of the week, the time I went to sleep, and whether the instance of sleep counted as a nap or bedtime sleep (see Figure 1). I then catalogued the number of hours slept, my mood before and after sleeping, and my perceived restfulness (mood and restfulness were each measured on a 5-point scale).

Figure 1: Excerpt from Data Set

Restfulness and mood were similar but slightly different measures. Restfulness captured if I felt groggy upon waking from sleep. Mood, on the other hand, was a more comprehensive variable that also took into account my emotional state (which was often influenced by how well-rested I felt). Finally, I noted where the sleep took place and whether I used an alarm to rouse myself. However, I did not end up using these latter two variables in my visualizations because they did not show much variation. (I.e., I tended to sleep in my bed and to use an alarm most of the time.)

Visualizations

Figure 2: Time Series

Figure 2 (below) provides a two-week cross section of my daily rest. On average, when you combine time slept at night and during the day, I slept 10.4 hours a day. This may seem quite high–in fact, the NIH indicates that the average adult should be sleeping only 7 to 9 hours a day. However, I suffer from excessive daytime drowsiness, so 10 or more hours are what I need to feel well-rested.

Furthermore, my total sleep was lower on days where I didn’t nap, which tended to be Mondays (e.g., March 24 and March 31). Total sleep tended to be higher on Fridays (e.g., March 28 and April 4), which represent the start of the weekend (meaning that I can sleep more if I so choose). Notably, I never got less than 8.5 hours of sleep a day during this period because I did not feel I could function otherwise.

Figure 3: Tree Map

To understand how the quality of my sleep differed daily, I averaged my scores for restfulness on naps and nightly rest each day (see Figure 3, below). Each day of the week is pictured with an associated restfulness score out of 5 (with higher numbers indicating enhanced restfulness). 

Overall, my scores ranged from about 3.2 points to 4.9 points. That means I had pretty close to a perfect sleep score on certain days, and an above average sleep score on others (with average being 2.5 points). 

This tree map uses size and a graded color scale to provide a sense of which days tended to have the most restful sleep–which are Saturdays and Fridays. It makes sense that I received the best rest on those days because those are weekend days, so I can sleep longer if I so choose. By contrast, my lowest average restfulness scores are reported on Mondays and Tuesdays, which represent the beginning of the week when I am scrambling to accomplish tasks and don’t have the luxury of resting as much as I would like.

Figure 4: Pie Chart Multiples

I then wanted to understand how much of my total daily sleep is accounted for by naps. Through a series of pie charts (see Figure 4, below), I realized that I napped nearly every day in my sample (the orange slices represent days with naps). The only days I did not nap were March 24 and March 31 (both Mondays) and April 1 (a Tuesday). This aligns with my earlier observation that I tend to have less rest at the beginning of the week.

Interestingly, my naps tended to pretty consistently make up 11% to 25% of the total time I slept each day. That means that my nightly sleep usually accounted for 75% to 89% of my total daily sleep. Naps are truly a crucial part of my sleep regimen and are key to me getting enough sleep per day.

Figure 5: Bar Graphs

Given how much I was napping, I wanted to understand if my mood was positively or negatively affected by my napping habits (see Figure 5). (Note that the dates March 24, March 31, and April 1 are omitted from the graphic because I did not nap on those days.)

Across the board, I woke up in a better mood after a nap than I was in before I took the nap. There was never a negative change in my mood due to a nap. Instead, my mood tended to increase anywhere from 0.5 to 2 points on the Likert scale. This is probably why I continue to take naps–because they are associated with positive feelings immediately afterwards.

Figure 6: Slope graphs

At this point, I wanted to explore whether my mood upon waking was correlated with the duration of the sleep. In Figure 6, I present two slope graphs, with the blue line representing nightly sleep and the orange line representing instances of naps.

Once again, I found that my mood always increased upon waking up from naps, no matter the length of the nap (although my naps were never shorter than 1 hour). However, for bedtime sleep, my change in mood was very dependent on the number of hours slept. If I slept less than 9 hours, I generally woke up the next day in a worse mood than when I went to sleep. However, if I slept more than 9 hours, my mood increased up to 1 point upon waking. It makes sense that I often woke up from bedtime sleep feeling poorly because otherwise I would not be supplementing my nightly rest with naps!

Figure 7: Graduated Symbols

Figure 7 (below) explores whether naps might be having an effect on the time I went to bed each night. Note that, in the sample, I tended to go to bed at midnight at the earliest, so I treated that as my baseline bedtime. Of the 14 days in the sample, I compared my nightly bedtime on days where I didn’t take naps (blue) and days when I did take naps (orange). One limitation was that there were only 3 non-nap days to compare, so this wasn’t a perfect comparison.

On the days where I didn’t take naps, my bedtime ranged from 12:00 AM to 1 AM. But, on days where I did take naps, bedtime could be as late as 2 AM. In fact, I slept at 2 AM 18% of the time on days where I took naps. I also slept at 1:30 AM 27% of the time on days where I took naps. It makes sense to me that I would go to bed later on days where I took naps because I felt better rested and less eager to sleep at night.

Figure 8: Line Graphs

Finally, I filtered my data to only look at nightly rest on each of the 14 days in the sample. I wanted to separate my data into two categories, again–days where naps had been taken (orange) and days where naps had not been taken (blue). I wanted to understand if the quality of my nightly sleep was impacted by whether I took a nap earlier that day (see Figure 8).

Interestingly, I found that my mood was much more variable upon waking up from bedtime sleep on days where I had napped. It was a toss-up as to whether I would feel better or worse after waking up from nightly rest.

However, on days where no naps were taken (blue), I always woke up from bedtime sleep with a mood that was equal to or better than before I went to bed that night. If we are using mood as a proxy for restfulness, this supports a theory that naptime degrades the quality of nightly rest.

Discussion & Conclusion

In this project, I learned the following:

I sleep an average of 10.4 hours a day when combining time spent napping and nightly rest. I tend to nap on most days, and on those days, naps can account for 11 to 25% of my total daily rest.

I get the most rest on the weekend (Fridays and Saturdays), and the least sleep at the beginning of the work week (Mondays and Tuesdays).

As long as I take a nap of at least 1 hour, my mood upon waking will always be better than it was before I took the nap. However, for nightly rest, sleep needs to last at least 9 hours for me to wake up in a neutral or better mood than when I went to sleep.

Bedtime trends later on days where I nap. Furthermore, I am more likely to wake up in a negative mood after going to sleep at night if I had napped earlier in the day. If I did not nap earlier in the day, I always awoke from bedtime sleep feeling either the same or better than when I went to bed the night before.

However, this data is not without its limitations. First of all, this “experiment” was not a true randomized-control trial, so I have no way of knowing if my findings were random or truly reflect how I experience sleep each day. Second, I had to self-rate my mood and restfulness, and on many days I struggled to decide which number on the scale to assign. Finally, I tracked both self-rated mood and restfulness, but my answers to these metrics tended to covary–so I might as well have picked just one to measure.

Ultimately, this project confirmed many of my hunches about how much I sleep, the importance of naps, but also their potentially harmful effect on the quality of nightly sleep.