We all know people who sleep like rocks regardless of how stressed they are, while others lie awake, feverishly counting sheep when they feel under pressure. New research published in Emotion may shed a light on why: People with specific personality traits may sleep better in the face of stress.

Researchers designed two experiments to study how specific traits are related to stress and sleep. They looked at short and long term stress — like the anxiety that comes the night before a presentation, for example, versus day-to-day worries — and studied a population known for being both stressed and sleepless: college students.

First, the researchers followed 99 Carnegie Mellon students for 6 months leading up to an exam. They asked the students questions about their personalities and sleep patterns, measuring both sleep quality — like how many times you wake up during the night and how well rested you feel in the morning— and sleep efficiency, meaning how quickly and consistently you fall asleep at night. They found that before a stressful event like an exam, the trait of vigor — defined as being lively and energized — predicted better sleep quality.

Perhaps even more interesting is that students higher in the trait of calm — think, your friend who is always relaxed — got worse sleep before the exam. The researchers suspect that calm people may be, well, too calm: If you’re ultra relaxed leading up to an exam, you may not prepare ahead of time, leaving you cramming the night before.

A second experiment (also with Carnegie Mellon students) echoed the findings from the first: Calm people didn’t sleep as well in response to one-off stressful situations. However, when it came to day-to-day stress, calm was helpful for sleep. The researchers also found that vigor and overall well-being were strong predictors of sleep efficiency, and the effect was even stronger in high-stress times.

What the researchers don’t know, and want to find out, is whether personality is merely linked to good sleep or if it actually acts as a buffer keeping stress with messing with rest. However, the findings are an important addition to existing studies on the relationship between sleep and stress, and a reminder that if you don’t consider yourself full of vigor, prioritizing your overall well-being can still help you get a good night’s sleep.

Read more about the findings here.

Originally published at journal.thriveglobal.com