Has anyone else experienced this before?
Yeah, every time my shite makes me nervous!
Seriously! I tank for a bit when I work with someone new that I'm nervous about, till I settle down and get comfortable with what they are going to do. I tend to tank a bit for *really* big muscular guys who throw without taking my balance first (rather than going splat when they throw me anyway).
The really serious training begins when I know someone and trust them enough *not* to tank...with some that's as soon as I step on the mat...with others that's never.