That's normal, believe it or not.
Doesn't happen anymore, but in the beginning, if anyone were to see me, they would have probably called 911 thinking I was seizing. The best thing you can do is go with it.....just let it happen. It's supposed to. It's cleansing.
And yes, too many guys just don't give it long enough.....I get it.....but it's the only thing that's gonna do it.