I find that I can drop off to sleep quite easily, but then wake up and can't get back to sleep again, and have tried all the usual, like not staying in bed, or reading for a while etc, but then I'll drop off for an hour or two round 4am, but still wake up quite early too, and feel tired for the rest of the day. I try not to sleep during the day but I find that as I get older I often have a cat nap in the afternoon - I just feel my eyelids dropping and I'm out for half an hour or so!