Wake up after 3 or 4 hours with CPAP and can't go back to sleep


I have been on CPAP for only a few weeks, and I am still getting used to it.

I have noticed over the last few nights that I tend to go to sleep fairly quickly now (while it was a struggle when I started CPAP) but only stay asleep for 3 or 4 hours. I therefore wake up at 1am or 2am, quite refreshed and feeling well. However, I struggle to go back to sleep with the mask and machine on, so I go back to sleep without CPAP, and wake up more tired.

Is this usual?

I am assuming 3 or 4 hours is matching a sleep cycle?