With a general anesthesia the patient is asleep and therefore doesn't move. With a regional block, you are awake but you are given drugs to sedate or relax you. Movement is possible, but isn't very likely.

Many shoulder surgeries are done now with the patient in a position seated as if in a beach chair. This supports your entire body without putting pressure on one side more than the other. The arm being operated on is placed in a special arm holder. Your body may be gently strapped in place to avoid slipping to one side or the other. A face mask may be used to hold your head in the middle.

Sometimes doctors will use a light general anesthesia along with the block. Talk to your doctor about your choices, especially if you are concerned about having just the regional block.