I'm have same issues with my 16mo son. I've been timing it, and it take about 12minutes for me to get him to actually open his eyes/wake up and stop crying and thrashing around. After he actually realizes I'm there, he eventually calms down soon after with some lights on and stimulation. Everything I've researched said night terrors don't usually start until there about 3 years old. I'm not sure what to attribute it to. I also just read an article recalling several batches of Hyland's Teething tablets, which where causing seizures. As a first time mom, I'm a wreck and not sure what's going on.
I am going thru the same thing with my 16 month old. Her thrashing and crying was almost all night long. We needed to rule out seizures so we took her to a Ped. Neuologist and they did a EEG. The conclusion was that she is suffering from severe Night Terrors. There is not much that can be done, other than trying to control her enviroment and keeping her naps and sleep schedule regulated. The worst nights are when we have busy days and naps are not so good. Hope this helped, and Good Luck!
Really hard to tell if he's seizing based on the info. He may be having night terrors, nightmares. The only way to know for sure if he is having seizures is to do an EEG asleep and awake.