Well, as a confirmed "sleep downstairer", I was forced to try the upstairs option following the tragic demise of my favourite airbed.
I have now slept both ways.
I have no problem with the claustrophobia, what I do have a problem with is the light position.
Sleeping head-first to the hatch filled me with complete illogical trepidation, sliding head first into a crumpled undignified heap on the front seat, but spookie's suggestion of raising the head end of the mattress has proved brilliant.
Sleeping head to the hatch has problems for me as I may need to make a very quick exit. No, it's not a woman age-thing, it's cramp. I am prone to nocturnal cramp in my calf muscles, especially if I have been doing a lot of running or hill walking. The only remedy is within seconds getting the foot of the affected leg on a hard surface and putting all my weight on it, otherwise it's excruciating pain and possibly a calf muscle in spasm for the next couple of days. Extricating myself from upstairs, head to the hatch position, would be difficult.
Tonight will be the test. Walked the 12 miles between Westward Ho and Clovelly and legs feel like lumps of knotted iron.