Water has a significant effect not only on our body but the mind too. It's one of the reasons People feel attracted to the moon as it affects Water heavily.
No matter how strong you are, Water can create heavy pressure on the body and mind. Experiencing a Tsunami in your dreams means you are under some mental or physical force.
If you encounter such dreams, try to find out the cause of stress and deal with it, as dreams are a warning sign you must not avoid.