I Have Woken Up In The Middle Of The Night

I have woken up in the middle of the night for the past 3 nights...with the feeling that I am going to fall or roll out of bed. Can't go back to sleep for 3-4 hours. I Think it's something with my equilibrium. What could be causing this? I do have sleep apnea and sleep with a cpap, but have never experienced this in the past 5 yrs of wearing it...have actually slept great up until 3 nights ago