I feel your pain. I've fallen asleep (when I was working) in the middle of typing and then woke up and see I typed more than I remember typing. I've fallen asleep while eating, while on here, in the middle of reading, on the loo.....etc. But I go to bed and I'm wide awake. When it happens it usually hits pretty fast. It's one of the many reasons I won't drive very far from home and sometimes not at all. I was once scared I had narcolepsy, but my issues seem to happen with extreme stress and several nights of issues sleeping and staying asleep. If I am having good days I never have these sleep attacks.
I haven't done any sleepwalking though.

I looked into Sam-e but it is rather expensive. Right now I am taking a multi vitamin called Fibro-Response it has magnesium, GABA, MSM, malic acid, D3, C and all the Bs which are all recommended for us. It costs me about 26.00 a month. And has a lot more than I mentioned. I usually buy it off amazon or iherb, whichever is cheaper at the time. The only down side so far is you take 3-4 pills a day and they are vitamins so they taste bad and are huge. The malic acid and MSM are supposed to soothes muscles and joints. Not sure yet if they do, but I haven't been taking it long.

Ask for a sleep study. See my answer above.

I have taken Ambien as well. I started with regular Ambien then it stopped working. I was given Ambien XR. It does help sleep, I just like to give my body a big break in the summer and only take it when I am desperate. Very rarely it didn't work. If I ate too late it definitely did not work or if my anxiety was too high.
In the winter I notice my energy is low (maybe from the chronic pain). That is the reason they also gave me Cymbalta which works great to give me that energy I need for the day. I am not taking that now. But I want to try Sam-E and see how that goes.

I told mine, that was why he put me on Ambien. Before spending time and money on a sleep test, he wants me to try to get on a schedule (yeah right) and get some real sleep and see if it still happens. And I usually only snore when I have allergy issues and have to breath through my mouth. My mother has heard me sleep a lot and she says she has never heard me stop breathing. She would know too, she had spent years listening to my dad stop breathing before we finally convinced him he needed to talk to a doctor. He has a C-pap now. Now it could be possible I need a Bi-pap, I do tend to go from very shallow to very deep breathing so my oxygen levels vary widely when I sleep. I have been told that is likely due to my allergies and asthma. I guess, I am in wait and see...now if I can just get disciplined enough to take my ambien at the same time every night.