Sleep Alertness/Sleepiness

Having a good night of sleep is key for alertness, our ability to maintain attentive wakefulness during the day. In fact, some studies suggest that being awake for 17 hours is the equivalent of having a blood alcohol concentration of 0.05% (i.e. a state similar to what we experience after having three alcoholic drinks), whereas 24 hours of wakefulness raise that to 0.10% (equivalent to five drinks). Poor sleep can lead to loss of energy and motivation, sluggish reactions, and higher risks of making mistakes. Conversely good sleep helps restore the brain by actively cleaning the harmful chemicals we accumulate in our brains across the day, so that we have sharper thinking skills the next day.

We normally experience some variations in our level of alertness across the day. There are some indications that alertness may cycle through peaks and valleys about every 90 minutes, although the specific lengths of these cycles can change from one person to the other. This is driven by fluctuations in parts of the autonomic system that promote arousal (e.g. peaks and valleys of heart rate and respiration). Most of us also tend to experience a temporary increase in somnolence, with decreased energy, lower focus, and poorer performance during the mid-afternoon. Although this is called the post-lunch dip, this happens regardless of whether we eat or not. Yet, it is worthy to note that a heavy high carbohydrate lunch can make this worse.

Conversely, lower alertness and higher sleepiness are necessary to fall asleep. Most of us have experienced some nights when our mind keeps racing after we shut down the lights. Sometimes this is because we worry about something, but sometimes our brain is just overly active. In these instances, we may become overly preoccupied about how we will manage to pull through the next day, and this can be a sufficient source of worrying to make it even more difficult to fall asleep.