My husband thinks my 4 year old may have ADHD.?

My son just turned 4 in July. Just recently he has been suspended from pre-school for the second time. The first time was 4 months ago. After a bad week and a phone call from the teacher, he was climbing on bookshelves and struck the teacher when she tried to physically remove him befre he hurt himself. That was the first time that we had ever been exposed to him acting like that. My husband and I strongly believe in discipline and he definalty does not act like that at home. This time he had a bad week with talking back and rudeness toward the teacher. Then he just exploded. I watched him on the camera playback as he proceeded to jump around the clroom during rest time distrubing all the kids who were napping. He climbed on the table and threatened to jump on a sleeping child. I ws brought to tears as I watched my respectful little boy terrorize his cl. The teacher just moved everyone away frm him. When the director was called in to take him out, he took off and began to run around the school. He even tried to get leave the building. Now I am not making excuses for his behavior. It seems that naptime has been when he blows up, at least for this past week. My husband thinks that this may be an early sign of ADHD. He gets extremley frustated when he can't complete a task. Such as oning his pants, shooting his ball, zipping his jacket, etc. He has so much energy and is always moving when he's not eating or coloring. He never walks. To top it off his biological father has ADHD, anger issues and is bi-polar. I on the other hand am not so quick to say there is something medically wrong with my baby. To tell the truth the first blow up happened shortly after my mother had movd in with us. She has a discipline style that is totally non-existant. Now that she has been gone for the past week or so, the behavior has reappeared. I don't know. Any suggestions or similar stories. I want to know if we should look into this because they are trying to suspend my baby. SO EMBARRASING!!!!!!!