Re: Ukemi and Dizziness
It could be many things:
Simply not used to rolling. I've been doing aikido for about 10 years and if I have an extended break in training I get dizzy doing ukemi for a few classes until my body adjusts.
Could be something you are doing wrong in your ukemi: one hint many people seem to suggest is the pick a point on the opposite wall and concentrate on it before and after your roll...I believe the thought behind that is to have a common frame of reference helps your body orientate itself.
Physiological: maybe your body just isn't cut out for that kind of movement/change in elevation etc. Do you get carsick while a passenger or while reading in a moving vehicle? Maybe meds like Dramamine will help.
I hope this problem gets sorted out for you...its definitely no fun. Like David and others mentioned...go see a sports medicine doctor or a kinesiologist. Maybe even hit up a local university's student medical college to do it 'on the cheap.'