[Martian Tigress]

Physical defenses are lowered at night. During REM sleep, your body's ability to move is disabled, which is why most people aren't sleep-walkers. Production of hormones that help keep 'daily awakeness' organized are also lowered. The body needs a chance to recoup, and this is part of the reason for sleep.

What I have mentioned here is only the tip of the proverbial iceberg. There are many body functions that are governed by circadian rhythms, and their functions peak during the day and trough at night. An example of this is kidney-function, which is higher during the day than it is when one is asleep. This prevents people from having to get up a lot during the night to relieve themselves, which in turn, means that the deep relaxation into REM sleep is more protected.

The body also does a lot of things biochemically to prep for/come out of sleep. I'm not going to list everything here, but one obvious thing it does is drop your core body temperature by about one full degree (body temperature peaks in the afternoon, which is when and why fevers 'spike' when one is ill). How the body does this is complex, and I won't go into that here. The bottom line is, the fire of metabolism burns less brightly at night.

What this all means is, key portions of one's physical defense-system are 'turned off' entirely or slowed way down at night.

Peace,

Martian Tigress