i go through patterns where this happens to me also. sadly i'm only able to fall back to sleep just as it's time to get ready for work....i absolutely HATE that. but when i go through these patterns, there's usually some stress that's causing it....and it's almost always work related.
do you have problems actually falling asleep? if so, you should try to identify those problems. mine was always racing thoughts...usually work related. if something that you can identify is preventing you from falling asleep, then it could very well be what's keeping you from sleeping all night. it's just a thought, though.
I agree with green lydia, how has this progressed?
I'm not sure if your sleep problem is caused by anxiety, but the fact that you are obsessing and worried about it seems to be creating an anxious state for you.
What happened a month ago when your sleep pattern changed? Cast your mind back to that time and really try to figure out what was going on in your life then. Did something happen? Did you lose your job, break up with g/f......b/f? Get sick? Did someone, God forbid, die? Did you move? Begin or stop a medication? Something happened, and you need to figure out what it was. Could it be something simple like construction going on near you that is causing or caused you to wake early?
My advice, when you wake up, GET UP! You say you fall in and out of sleep for the next 2-3 hours and then wake up groggy. That is usually a sign that you've overslept, which is why the sleep "experts" advise us to keep to our normal sleep schedules even on our days off. They also advise that we go to bed at the same time every night and have a sort of "I'm going to bed now" routine. Surprisingly, they recommend that you DON'T exercise before going to bed. They believe that gets the "juices" going and isn't conducive to sleeping. They say if you watch TV before bed, don't watch the news or some crime show...........instead, watch a comedy show. Or read a good book If you've been waking up after 5-6 hours of normal sleep, maybe your body is telling you it's had enough......even if that isn't what YOU consider enough or what is "normal" for you. Our sleep rhythms do change. Perhaps that is all that is going on with you. I'd try getting up and doing your usual morning routine, see how you feel the rest of the day. If you feel very tired in the afternoon, take a nap, but don't sleep more than about 15-20 minutes. More than that, and you risk messing up your nights sleep. Do this for a few days and see what happens. Maybe your body just needs it's "clock" reset............or maybe it only needs 5-6 of sleep right now. We are all so different in the amount of sleep we need to feel our best. But obviously, when you stay in bed and sort of toss and turn for those few extra hours and wake up feeling groggy, you aren't feeling your best, so try changing things.
If this doesn't work, then it may be time to have a chat with your doctor.
Good luck!
Peace
Greenlydia