Yeah definitely. I can tell that they're talking to me but I can't make out the words properly. I'll have to remove at least one side to listen.

I've worn IEMs for hours on end for many years, and I don't think I've ever had that "underwater" experience as you mentioned.

Maybe only with some really cheap silicon ear tips. I tend to prefer foam ones.

I guess it differs from person to person. For me, it's perfectly comfortable once I get the right size ear tip in. It's snug and I forget they're there after a few minutes.