I also have this happen. The neuro that sent me to UT Southwestern treated me 8 years ago for a tremor (legs, arms, neck) they thought was MS. Turned out to be a horrible side effect from an anti depressant my PCP had put me on (needless to say I no longer take any of those). It took almost three months to get back to almost normal. When he saw me in September he said it looked like a residual effect from 8 years ago that will never go away (?). Most of the time now my muscles will usually give out before the tremor has a chance to come up. Although my neck will feel shaky and make my head tremor. Never have had my head drop. I usually lean back in chair for awhile when it starts this or lay down.