Odd 2 1/2 year old tantrums?

My son is a sweet, mellow, reasonable little guy. For the past week, however, he has had several really scary meltdowns over "nothing" - tonight, for instance, I calmly told him not to throw a toy. He got so angry that he didn't know what to do with himself - he was writhing on the floor screeching and crying. He didn't want me to touch him - kept saying "no, momma". Nothing helped - the more I talked to him the angrier he got, and he didn't want me to hold him but he also didn't want to be put down. He kept walking from room to room (or while I was carrying him pointing all over the house wanting me to go there). He didn't know WHAT he wanted. I finally just put him in the bathtub and he calmed down (after throwing a few bath toys in anger). I thought he was going to hurt himself the whole time - he slammed his knees on the floor, etc. Does this sound familiar? Should I be worried? His meltdowns are so frequent and not because he isn't getting something he wants - I honestly don't know why he's so upset. He's good at communicating - it isn't that kind of frustration. He is scary to watch - like a little caged/enraged animal. Any thoughts? Thanks!