During this time, the blood vessels or arteries are active. This means any health problems associated with the immune system, thyroid, adrenals, or metabolism could be keeping you awake. (source)
Stress, paranoia, or confusion could also be keeping you awake. If you find this to be the case, try some meditation, do a bedtime yoga routine, or repeat some calming mantras.


Waking Up Between 11 PM and 1 AM


This time is associated with the gallbladder. This part of the body works to break down all the fat you’ve consumed during the day. Waking up during this time could mean that you need to switch to a diet with healthier fats. (source)

However, if you are experiencing feelings of judgement towards yourself or others, or resentment, that may be keeping you up as well. It is important to let go of the mistakes you or others have made and expel resentment. Acceptance and forgiveness are important.