Irregular sleeping hours is widely reported by PCS people.

I JUST STARTED this, a little bit back last Week (8) and now this Week. For example, Wed. I slept well, getting near 8 hours (which actually I think is more than I need). Suddenly on Th. and F. I struggled to fall and then stay asleep and only got somewhere around 5 or 6. Sa. I slept another 8 but the next day felt tempted--resisted--to nap during the day. The two periods feel different (see also my 'Journey' thread): during the difficult sleep period I develop this odd dread as the day nears the end. During the easy period I feel relaxed and maybe a bit too hyped at times, but closer to my normal self. Though it's not unusual to have stressed periods, the way these two conditions flips back and forth is abnormal.