My 89 yr old mother falls asleep on the living room couch several times/day. When she's awakened, she claims she can't move. Any ideas?

She flops like a (heavy) rag doll, and shrieks if we touch her; refuses to try raising her arm when I try to give her medication. Waking from bed in the morning, she's okay. And once we get her moving, she's all right. It's almost like sleep paralysis, except no hallucinations. She was recently Dx with sleep apnea, so her night time sleep is poor, though how that could cause daytime sleep paralysis, I can't imagine. Has anyone on this forum experienced something similar?