...when Marty started shaking and trembling during the concert scene because the past was being altered? I don't know, it just reminded me of Michael J. Fox's current struggle with Parkinson's disease, since the movements reminded me of that. So sad to see him move like that knowing that he would get Parkinson's much later in life.
shareI think making this movie is what helped bring it on. He was shooting Family Ties in the daytime and BTTF at night. For however long it took to shoot this movie he was going on 1 hour of sleep per day! God created our bodies to sleep so they can get rejuvenated and repaired. That much lack of sleep for that long (several months?) is detrimental to one's health!
shareThat's right @muchmeow, and he also got strangled for real, making BTTF III.
When he is hauled up by the rope round the neck (and Doc shoots the rope, setting him free), he was accidentally left hanging longer than he should, and he blacked out. Pretty sure that can't have done his brain much good. Asphyxiation can cause permanent brain damage.