OK, I know this is a naive question but DD is my first and I don't know many other babies/toddler 
DD is about to turn 17 months, and is normally a joy, if determined about how things should be. At bed time two days ago, and for this morning's nap, she's had absolutely thrashing, screaming hysterics, to the point where I haven't been able to hold her. I don't think she's in pain, because she's giving off her tired signs - ear tugging etc, - but has reached such a fever pitch of screaming that we haven't been able to comfort her.
Today I left her in her cot, as she was in danger of throwing herself out of my arms, where she kicked, waved her arms, threw dummies and teddy about, and banged her head on the bars (not sure if that was deliberate, but it gave an extra spice to the howls....). I sat in the chair beside her and when she started to calm a little, after about 25 minutes, I picked her up, rocked and shushed her, and she fell asleep so soundly that it was like passing out. Normally she's pretty good at being put down awake and going to sleep herself, and we keep a pretty definite schedule as that's always been her preference, so I'm not sure what's going on.
Does this sound like a tantrum? And if so, what's the best way to handle it when she reaches the inconsolable stage - trying to hold her seems to wind her up more, and she fights so hard that I'm worried I'm going to bruise her, but I don't any her to feel abandoned when she's clearly so distressed. Is 17 months too young for this sort of behaviour? I thought it was the terrible twos?!