Hey sorry to hear about your snake. My guess unfortuently would be you just had a snake with OMPV, the symptoms all point to it. And unfortuently there is a lot of it getting around, I know a lot of people push it under the rug and that's the reason for the bad spread because these people still sell there snakes. The fact of it's mouth open, limp, no direction in moving it' head, the lump can actually be from loss of fluid as the disease ats rapidly so it's muscle that your seeing as a lump. The normal signs of OMPV are first lack of tongue movement, either not drinking at all or the complete opposite compulsive drinking. Sometimes you can see mucus in the back of the throat, they can either go right of there food or normally eat then next meal regurgitate than won't eat there after. It's a fast acting virus, usually they go from fine to dead in a month, but depending on the time of year temps etc such as cold can sometimes slow the virus down. Unfortuntly though with all the signs most people don't catch half of them. I just hope the snake was no were near the rest of your collection as I'm almost 95% positive you've just had OMPV in your collection. I would also get in touch with the person you got it from, the possiblity is they will deny ever having the disease but the more people that are open about having or had this virus the less of us there are going to be out there loosing out beloved snakes.
Allana