Hmm it could be any reason, but did you slept during the day like a nap? Because that can mess up my ability to go to sleep.

However there is one way that many people forget when they have trouble falling sleep. You know the way you close your eyes when you try to go to sleep normally, you somehow intituvely know how to do when you try to go to sleep. Hard to explain but you maybe understand what I mean. Anyway if you move upon awakening try to do that falling asleep procedure for just a few seconds and then stop yourself and try to be aware, that way you can induce all the strange sensations that come right before a dream and actually use them to enter one!

It can of course also be used to fall asleep unconsciously if that's your goal