I was a lifeguard for years in my youth and have rescued maybe a dozen people, most of whom could swim. The truth is that some people just lose their presence of mind when they encounter an unexpected situation the water, and in their panic they even forget how to swim or save themselves.
You’re right...Had the same experience....kinda lost my bearings. Next thing I knew I was laying on the side of the pool. The lifeguard was really alert. The next week, I received my Life Saving Certificate.