I have had many severe seizures that have caused all of these symptoms except for the drooping of the face. That sounds more like Bells palsey to me. The facial drooping could be part of what is causing the speech impairment too. I have had seiz. in which I didn't regain full speech, memory, or strength in one side of my body for several days.

I don't know if Bells palsey is ever related to seizures or not. Has your son had an EEG or cat scan or MRI? A cat scan or MRI may be able to rule out or confirm a stroke. You didn't mention if his leg is affected also. With a stroke the entire side of the body is affected.
Hope this helped and good luck. Keep after the doctors till you get answers.

Unfortunately it is a slight possiblity. From what I read & heard it is rare. But if a seizure goes on for too long it could be an end result.

I have had this happen to me this week,my doctor told me it's called Todd's paralysis,and the resulting weakness (mine is on my right side) should pass. He has given me a 2 week course of prednisolone to aid recovery....I hope this helps....