Have you ever done underwater diving?
I've done it a few times, but I didn't go too deep. The high ambient pressure limits how far down you go, unfortunately.
It sounds so interesting.  I have never done it but would definetly be interested in it.  I bet the things you see are beautiful
It's beautiful, but requires a fair amount of training to learn how to use the diving regulator to reduce the pressure of your breathing gas.
Yes, I would be so scared I would forget something vital while I was down there.  
If you're scared, you could try scuba diving which uses a self-contained apparatus and is easier to control.
I wasn't aware that scuba diving was different than underwater diving
Scuba diving
Scuba diving is a mode of underwater diving where the diver uses a self-contained underwater breathing apparatus (scuba), which is completely independent of surface supply, to breathe underwater. Scuba divers carry their own source of breathing gas, usually compressed air, allowing them greater independence and freedom of movement than surface-supplied divers, and longer underwater endurance than breath-hold divers. Although the use of compressed air is common, a new mixture called enriched air (Nitrox) has been gaining popularity due to
the sort of thing I used to dream about, so I practically bit their hands off, of course. No writer turns down a brief like that, regardless of what else you have on. It'll be £2.99 and I hope to see it stuffed dog-eared into a few back pockets. It is darker in tone and plot than anything else I've done, but to explain how would be to explain all. It's coming out next year - in March, I think." - Conn Iggulden