Hello Hope! That name sure has a special ring to it!
I think if you suffer from CP and your working, then from experience at least for me, the answer is...certainly an afternoon sleep attack can visit you.
There are several other things that can cause, this sleepiness you suffer...one being boredom...and then maybe stress...or being on the down cycle of BT pain med's.
Is it possible that any of things might be the culprit?....maybe a combination of the three?
Several of the members have made excellent suggestions...but one stood out to me..and that would be White Beards suggestion. I think over 50% of at least Americans suffer from Sleep apnea.
I have too!...have not slept well at all in several months, and wonder if I suffer from the same thing. Probably a Dr's appointment in in order then.
Good luck to you, and I hope you find the culprit that is robbing you of an energetic day. It can be miserable to say the least.
SE