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Yes I get this a bit after flying, but more so after being on a ferry. Not when sleeping though. I have no problems during the actual journey, but suffer a moving sensation for a few days afterwards. Once after a rough overnight crossing, I was dizzy for a whole week after, almost falling over several times and having to hold on.
Still don't have a cure though. Have tried sea sick tabs and wrist bands, neither of which made a jot of difference. I have suffered inner ear infections in the past with similar results, so maybe I am just more prone to it. Luckily I'm not a jet setter and don't travel that much.
Could be labyrynthitis - inflammation of the balance mechanism of his inner ear. The pressure changes caused by flying can set things off.
My friend ended up crawling off the plane and spending the next 2 weeks in bed. OK, it was his honeymoon so they'd been planning to do that , but evrytime he moved afterwards he would feel really dizzy and sick and have to hold onto the floor so he wouldn't fall off.
I did after being violently ill on a flight home a couple of years ago. Went to Docs and he gave me stemetil, I now swear by them and have not been ill since, even flew to Australia and back with no problems. My DH suffers too if he does not sleep on the plane or coach etc but usually wears off after a couple of days.