N.S.
Oh, I can empathize!
Our 18 month old when through the same thing. We did the following, which seemed to help:
1) we got him naked and put him in the bath with his toys with NO WATER. We let him play for a while and then gave him a bucket with water and other cups so he could pour. We kept on giving him full buckets of warm water to pour in and out of cups until he was sitting in about an inch of water (it took a while for him to fill the bath that much).
2) the next bath we did the same thing
3) the next bath, we introduced bubbles and put in about an inch of water with about an inch of bubbles. He tolerated that water.
4) we slowing increased the amount of water with bubbles in the tub and after almost 3 weeks were able to pour water over his head to give him a shampoo.
Good luck. Our little one now loves the bath like he did before the strange episode...although he still hates having water poured over his head!