What Causes Stiffness In Body While Lying Flat?

hi my name is clare i hope u can help me with the question i am going to ask u what it is when i lay down flat mi body goes in to like a fit all my body goes paralised i can not move my breathing go very slow i know were iam in my mind i just can not move any parts of my body at all i can have up to four of them in a night some times it can last up to about 5 minutes my partner is worried about me what could this be plus i have been getting a lot of headaches latley i suffer from asmmer plus i suffer with mentle health problems as welll as haveing a bad heart iam on on 4lots of medication iam on sleeping tablets depression tablets plus iam on methadone 2 inanlers please help me and tell what you think this could be