I've done Flexiril a couple times, but this will be a quick description of my first time.
Ok, first off, I consider this the best prescription drug I've ever consumed, besides Dilaudid (hydromorphone, basically the strongest pain killer you can get (except for the insane stuff you absolutely cannot get a prescription for, and they use rarely and only in insane situtations)), Morphine, and Phenobarbitol.
I consumed one 10mg pill and waited for the effects. I drank a light beer as well, then took another 10mg pill 15 minutes later. After about 45 minutes a lightness was coming over my body, and I felt very relaxed and happy. Things got stronger and stronger, and it was nigh-trippy at a few instances. After an hour and a half or so it got to the point where I was just in euphoria, giddily but subduedly remarking about how I couldn't move at all. It took about 10 minutes for me to finally get my body to move, and then I snorted about 10mg maybe an hour or a bit shorter than that after that. That hit me real hard, and things started to get very fucked up for me about an hour after that. My body and eye-lids weighed a bunch, and I was just sitting their staring, smoking a cigarette. Things sounded far away sort of and finally after a while I laid down and passed out.
Anyway, I never even had heard of skeletal muscle relaxers before this, and I can say that it is DEFINITELY more potent that Valium.