It will be good if you can keep a diary for two weeks and document the periods if your tiredness throughout the day and see if there is a fixed pattern. Consultation with a doctor who has special interest in sleep diosrders would also be useful.
The following disorders are known to be related to disturbances in natural biological rhythms are disturbed:
sleep disorders: Disruptions in the body’s natural rhythms can lead to affected sleep, including insomnia.
jet lag: A disruption in circadian rhythms when traveling across time zones or overnight.
mood disorders: For many patients wuith depression, their sleep is affected. They tend to sleep much later (phase delay). There are medications that can restore mood and sleep.
shift work disorders: When a person works outside the typical work day it causes changes in typical circadian rhythms.
Biological rhythm disorders can affect a person’s health and feelings of well-being. Some of the effects include:
anxiety
fatigue, tiredness, drop in mental alertness
daytime sleepiness
depression
lower performance at work
being more accident-prone
increased risk for weight gain
