This is a girlfriend of 10 years guys, that's not something you throw away just like that, not even for an outburst (which was completely wrong of her) like this.
That's probably also why he's fearing for a medical condition, I think he's got plenty of years of memories in which his girlfriend was caring and giving.
But Wally, you need to confront this, you know you do. This might be due to stress at work, it could be. But you've got to firmly tell her that you won't be treated this way because her work situation is lousy. You're there for support, if she wants a punching bag she should go to the gym and bleed of steam there.
A medical condition? I don't know, that seems more like an episode of a hospital series who seem to cope with interesting cases and rare diseases/disorders on a daily basis. But it might be the truth. Once again though, confront her. Explain the situation, describe what you believe has (violently) changed about her personality and see if she agrees, then you can go for appointments with doctors.
Sleeping in the jeep is not the answer and you know it. It's only a cool-down period and afterwards you can pretend that the problem 'really isn't that bad' or think 'I'd better see how this develops'. Make up a plan in your head for a talk and also for any option you can think of that might be the result of that talk. Up to and including making (mental) preparations on leaving her. If the talk goes wrong you should be able to act on it immediately (this also goes for a good talk btw).
Good luck.
