Pls give word to word meaning of the line - I struck at the water as I went down, expending my strength as one in a nightmare fights an irresistible force.
From chapter Deep water ,flamingo

Dear Student,

The story depicts how young William faced his fear when he nearly drowned in the swimming pool and overcame the same.
In this above line, he compares his situation in the water to a person who sees a nightmare and fights against it to the best of his ability but is still unable to forefend. When his feet touched the ground, he tried to leap and jump to come up to the water surface with the same force as one would try to fight against a dreadful nightmare. 


Hope it helps.
Regards