Cooldown with Efficiency V digging Underwater

When I start digging quickly underwater with my efficiency turtle helmet and efficiency 5 enchanted pickaxe, I feel a cooldown and I can never break blocks. There is no cooldown when I dig continuously with a normal pickaxe that digs slowly. When I feel cooldown I need to switch worlds and I can dig again. I hate not being able to break blocks again every time I quickly break 25-35 blocks underwater.