face spasm in my 15 month old, right side mouth and nose

5 days ago I saw a strange expression on my 15 month old son's face. His right cheek went in as if to smile and his nose turned significantly to the right like the nostrils were pointing toward the cheek - all this while his lips were apart. The spasm lasted two seconds and reoccured maybe 10 more times before his nap early that afternoon. In the pm no clear reoccurences were observed, but the following morning one minor event happened (without much nose deflection) and for only a short period (1 second). A second event occured during a diaper change when his face was otherwise relaxed and expressionless. The third day we saw an MD in our regular office, no health concerns were discovered and we were advised to continue to monitor it. The frequency had declined from day one as had the severity (3 minor events am day 3 & 2 minor events evening time. On day 4 in the am 2 full events occured with nose turning lasting 2-3 seconds, then no additional observed occurences. Day 5, two morning events one full & one minor, pm 1 minor. Some sleep patter change now observed, waking up once during night for a bottle & changing, not hard to put back to sleep. Looked at teeth last night - has 12 and 4 are just pushing through about 25%. The motion is smooth and no twitching is observed, he seems to be unaware that it is happening and it can happen while he is upset or while he is eating or while he is simply looking around. We don't know what the cause is or how serious a condition is or may lead to - does anyone know what this is or where to go to find out?
Thankyou for your consideration and expertise - Jeff