Experience Healing Sleep With Inclined Bed Therapy

I have been using Inclined Bed Therapy for 7 months, 5”. Prime reason for insomnia. I believe it helps to keep me asleep, but I wake up in the early hours, 3-4 am with my feet and lower legs off the mattress and I need to climb back to the top. Does anyone else have this issue? Any suggestions how to stay in the bed? My sheets are eucalyptus, not silky, the mattress is multilayer foam Nectar Premier. Platform bed, no boxspring. Any advice would be greatly appreciated!