I have had fibromyalgia for 5yrs now. ...For 5 months I have had severe muscle jerking when lying down. Is it possible to. Tx these?

Confirm the cause. Chronic widespread body pain is the primary symptom of fibromyalgia. The pain has been described as stabbing, deep ache, throbbing, twitching and others. The muscle spasm you are experiencing could be due to other causes as well, i.e. Restless leg syndrome, or a side effect of a medication. First confirm the source of the spasms w/ your md. If due to fm stretching as well as various meds can help.
Interesting Sx. ? how Rx muscle fasciculations in fibromyalgia (FM) sufferer "when lying down". Body on sleep surface torques shoulder & pelvic girdles thereby stretching nerve tracts originating in presacral & brachial n. plexi (possible explanation). Magnesium & calcium need supplementation? Ask pharmacy if OxyContin can cause. Topical cannabis & soft mattress might resolve. Walk & swim to build muscles.
Muscle spasms. Yes. Muscle relaxants do help. You have to rule out other reasons also. This include: low potassium, low calcium, dehydration, medications, restless leg syndrome and others...