I'll preface this response by saying that I'm not an engineer or home builder; just a homeowner who (like lots of others) have had to have a wall looked at to see if it's bearing. So just a "very" humble opinion!
A structural engineer (or architect) can analyze load factors and follow them down to your foundation. But in my experience, a good carpenter (someone who does serious remodels) can do just about as well. If it were me, I'd be tempted to ask around and try and find someone like that--since he/she'd likely be the one who could tackle fixing the problem anyway. I tell ya, there are pros out there who just seem to have a 'feel' for houses; they just glance at it and say, "yeah, needs a beam" or "no, that ain't nuttin'". The trick is finding one of those guys! (Personally, I wouldn't use a home inspector for this.)
I'm curious, have you:
--Measured the ceiling height across the room, to see how much (if any) it might have sagged? Or held a level to see how much it's off?
--Gone down to the crawl space and see if there's a big footing under the middle of the open area? If I were buying that home, these are just a few things I'd check (OK, as well as hiring a pro!)
I would think if the previous owner was any kind of engineer he'd have seen telltale signs of a load-bearing wall (such as joists overlapping the wall). But I've read accounts of even experienced people missing one of the signs.
Home ownership is stressful enough without having to be reaching for Valium right after move-in. It sounds as if this problem was disclosed (making recourse difficult against previous owner), and a home inspector may conceivably have missed the problem (if it's "hidden")--but some of the better inspectors may have caught it as well. Hopefully it's "just paranoia" and all turns out OK--and you can go back to having 'normal' home ownership for a while. Please keep us posted; the best of luck.