Re: Ukemi and Dizziness
People have gotten tissue scarring, and burst blood vessels from not fully exhaling. If you taste a little blood after getting winded you shouldn't be overly alarmed, unless you are spitting blood. But tasting blood is a clear sign that you damaged the blood vessels lining the inside of the lungs. It heels quickly, but if you cause a major tear you will need surgery to stop the bleeding.
For this reason I have no idea why anyone would ever teach you to hold your breath while taking ukemi. :/