I've done about 30 dives at all the popular sites and never experienced it either. Of course, always be prepared. Like Mike said, review your OW book and think over your course of action ahead of time so your not at depth trying to decide what to do if it does happen.
There are certainly more experienced divers than me on this board who have been in this situation before, but my thinking would be to resist the urge to drop your weights and instead remedy the situation by inflating your BC and swimming up. Once you get out of it, be sure to dump the extra air from your BC or you may end up heading to the surface too quickly.
The only situation where I would consider dropping my weights at depth would be if my BC was already completely full of air and I was kicking up with all I had, and I still couldn't beat the down current or get away from it. Once you ditch those weights you're in a runaway ascent. Not a good thing.
Most importantly, IMO, is to tell the DM exactly what your experience is and what your concerns are. That way they can keep an eye on you and/or choose sites that are in tune with your experience.
Since you're new divers without any overhead environment training, if you go on a dive with swimthru's, you should opt to go over the top of them rather than through them, and meet up with your group on the other side (the DM will explain this at the pre-dive briefing). Good bouyancy is a must for swimthrus.
I've seen divers go in, bump their tank, freak, then go vertical and bump their head, then freak some more and come shooting back out of the entrance like a bullet. Once a girl took my mask off my head with her flailing hands on the way out. I saw it coming just before she did it so I caught the mask as it came off my head and it wasn't a problem.
Ever since then, when I go through a swimthru, I hold up at the entrance just a second or two, to let a little distance get between me and the person in front of me to make sure they aren't coming back out the same way they went in, so it doesn't happen again.
Don't worry too much about it, just keep your head together and you'll be fine. You are gonna have a great time!