When you lifted off the gas you got the dreaded "tank slapper". You must modulate the throttle (ease back) in that case or go to full brake. The reason you went back and forth was because you unloaded the weight of the car from rear to front by snapping off the gas, thus putting all the weight on the nose and inputting the steering. I think you figured that part out. Glad you made it o.k. Remember in rain, you can always add throttle, but it's harder to decrease speed......