I have sleep apnea and sometimes don't get into the REM stage of sleep, where is where you get your rest... I usually wake up every 1 1/2 - 3 hours, so I take cat naps to try to get a little rest at a time... Sometimes I can sleep through the night when I'm wore-out tired....
I can usually sleep most of the night. Not so much last couple nights. Woke up early and often... But unless I am sick, I rarely sleep during the day. Once I am up and moving, I'm moving till sundown.