That's an interesting thought about the snake finally starting to feel better after years of neglect. I don't think he was neglected due to temperament - he was rescued from a hoarding situation where the person had lots of animals that they accumulated. Some were then flipped for money to get more animals, but all of them were pretty much ignored.
I've heard that Womas can be quirky and defensive, so maybe that really is just his natural behavior starting to come through. The seemingly sudden behavior change is confusing, but then again snakes can let things build up for a long time before it really manifests in behavior.
I just have zero experience with Womas. It sounds like the vet visit is in order but if he's in good health I almost feel like the focus should be on husbandry/enclosure adjustments and some regular handling.