My granddaughter, who is 18 months old, does all the above from time to time. She has normal social skills, interacts with other children, very expressive and great imaginative play skills. However, she seems to get overly excited or frustrated and does exhibit those behaviors above, especially shaking/trembling fists, trembling head movement, clenching teeth and fists. It doesn't last long and sometimes even laughs afterwards. I truly belive she is just expressing emotions without words and once she is able to put words to her emotions, she will grow out of the behaviors. I may see it twice in one day and then nothing at all for several days or weeks. I wouldn't get too concerned unless your child continues this behavior after he/she is able to verbally express emotions. Encourage him to use words or ask "are you angry?" or "are you excited?" My older brother used to hold his breath, along with his cousin, when he got upset and they would both pass out--part of the terrible twos. If your child continues beyond toddler-time, then having him/her evaluated by a doctor sounds like a good direction to pursue.