internal clock

My internal clock wherever I am just knows it’s 4 p.m. and I get a little sad.

When it is bright, our internal clock feels we should be awake.

Additionally, disruptions to the body's internal clock can affect astronaut's sleeping and eating cycles.

Prof Luscher said that - like the researchers suggest - it is "possible" that coffee drinking later in the day could disrupt out bodies internal clock at a time we should be resting.

You really have to be thoughtful of your act structures and that internal clock.