I joined the Navy wanting to do Flight Surgery. However, the last couple of years my motion sickness when flying has really worsened and if I don't take dramamine before hand I am wrecked with headaches/nausea/vomiting for days after. Even when I take it's not like I'm great and it does make me quite groggy.
At this point, I'm thinking UMO would be the move for me but wanted to get a gauge the amount of flying time during FS training and if it seems unreasonable to plan on doing FS and request a helicopter billet afterwards.
If it's as bad as you say, I would probably not go the FS route. You could consider trying to push through, but it would be tough. You would need a waiver, but they may prescribe you meds to get you through training. Depending on your seat in the helicopter, you can still get motion sick.
There is also desensitization training, which can be done at NAMI. But no guarantee it'll work. And the effects are generally temporary. You could try your own desensitization and essentially expose yourself to as much disorienting motions as possible. Right now, I think fixed wing training is 4 flights over 2 days (flight somewhere, land, and fly back). If you need to, the instructor pilot won't mind if you do nothing. But also, taking control of the aircraft can sometimes help with motion sickness.
Helos are 6 flights, I think.
You could also consider doing a drone squadron, or working at NAMI without being assigned a specific squadron. Also consider the aeromedical examiner route, where you go through NAMI, but without the flight training portion. Would not be a flight surgeon, would not be with a specific squadron, most likely a clinic billet.
