Every cycle has a rhythm to it, its own cycle. When I wake from a early morning nap (midnight - 7am) I usually start out a little tired, still wanting for sleep. That inevitably passes if I get up and start engaging my brain in something trivial like washing dishes or watching a tv show. Alertness follows for anywhere from 10 minutes to 3 hours. Eventually it comes back down, leading me back to sleep.
The sleep has its own cycle, from lying down to mental chatter, to unknowingly falling asleep, to deep dreaming, to non-REM unconsciousness, to gentle awakening. An alarm clock can interrupt anywhere in the middle of this, dictating the flow of the next waking cycle.
With the knowing that the tired feeling will pass if I just start moving, I now feel it's much easier to get up. I avoid productive work until the tired feeling is gone and replaced with alertness.
Somehow daytime is much different. It's more like one long cycle with just one peak and trough. It used to be more like night. But with the naps thrown in there it's actually much better than before. I don't know what I was ever thinking...being awake for 16+ hours with no sleep? No way. This is so much better.