They sound like common symptoms of being tired. The minds way of waking the body up suddenly, but can also occur when you are not tired at all. You sound normal everyone has it sometimes, sounds like you get it more so which could indicate that you are mentally tired but failing to acknowledge it or even when you switch off or think very hard. I highly doubt it is the beginnings of dystonia, unless you are walking along and suddenly stop walking and make a big out of control movement.