Rather than freezing, it might be that your game has entered turn-based mode without you noticing? It always seems to happen when the bulette travels around. You can get out of it by pressing the red clock button in the middle of your screen. I have no idea why it happens, or what benefit it is meant to give you, but it caught me out the first time.
Yes, I did get into turn-based mode, but I couldn't get out of it. The same happened in the Myconid colony, when I walked through a cloud. I mean, I think, it's normal to get some damage, but I wasn't able to do anything, move on or so. And getting out of turn-based wasn't working there either. I just save a lot now in the Underdark.