As an actor over the years, I have worked with a several people that remain "in character" from the moment they arrive in the theatre, through getting their costume and make up on, as well asevery moment back stage waiting for a cue, and remain so until they are out of make up, and even out in the parking lot after the show. They will not even respond to their own name, only that of the character they are portraying. To many people outside of the acting world, it is assumed that this sort of stance represents the pinnacle of the acting experience. However, I dare to say here in this blog that this total immersion in most cases is the more neurotic, and not to mention less effective way of doing things.
That is not to say I frown on being very focused and contemplative in one's preparations for a performance. (I myself am like that.) If, however, not enough of your mind is allowed to remain aware that you are in fact giving performance you invite a sort of mental absence. You abdicate a portion of responsibility to pay attention to the performance as a whole. You risk giving up the all-important total control over everything you do on stage.
Any dedicated actor can of course be moved at times by the drama and nature of a scene they are in. Many "lose themselves in a role", and this is a good thing. Yet there is a far cry between losing one's self in a role, and experiencing (or seeking to experience) a total possession of mind body and soul.
I remember my former acting professor frequently spoke of the dangers of allowing this. He mentioned a performance of a play (though which I do not recall) during the 18th century, wherein the actors portrayed patients in an asylum. So psychotic were they in their dedication to"feeling crazy" that the actors veered off the script, began jumping into the audience, and started a small riot. Whether or not the story is based on fact, the lesson is clear; remain aware of what you are doing. Do not abdicate your grip on reality just for the sake of a part.
Feel moved on stage. Weep, or laugh. Experience the joy, the tragedy, the grit and the magic of the endless worlds and the unlimited different characters the stage can offer. Certainly, make your performance come alive. Just be sure it is you, the actor, which holds the final reign over your mental faculties. Your performance will be better if you leave the door open at least a crack, on reality.
Plus you avoid being arrested for inciting a public riot. Everyone wins.