I've suffered from insomnia almost all my life, i can very rarely if ever fall asleep during the day even if i'm up all night....i just established a *normal* sleep at night of about 6-7 hours...I do not do any caffeine after noontime.
if your body is telling you something, listen to it, grab that quick snooze....but you might want to get a check up and some blood work to see if you may have anemia or if something is out of sync. too. and check your diet, vitamins, etc.
I just now feel strong enough(it will be 3 weeks quit tomorrow) and have started back to weights and next is cardio....but physically I am much more active and doing things than previously...just keeping busy and rediscovering/enjoying some hobbies I haven't done in years.
hope all goes well for you!