Let's see, were you going through your play lines with a dazed, faraway look in your eyes? Were you wide awake with excitement for your performance, or were you moving along as though you were sleepwalking through the script?
As a somnambulist, you'd be a sleepwalker. Sleepwalking, also known as noctambulism, is a sleep disorder that can pose all sorts of dangers for people who rise from their beds and perform some action (with eyes open) without recollection of what they were doing.
Sleepwalkers have been known to take a bath, eat a meal, change clothes, fire up the stove, drive a car, and even commit murder during sleepwalking episodes.
The mysteries of the conscious state make for great dramatic literature. Lady Macbeth's plagued with guilt over her involvement in the murder of Duncan when the stress pushes her into fitful sleepwalking.
In Act V, Scene 1, the Gentlewoman reports:
Since his majesty went into the field, I have seen her
rise from her bed, throw her nightgown upon her, unlock her
closet, take forth paper, fold it, write upon it, read it,
afterwards seal it, and again return to bed; yet all this
while in a most fast sleep.
And, from Joseph Conrad's Heart of Darkness:
The slim one got up and walked straight at me — still knitting with downcast eyes — and only just as I began to think of getting out of her way, as you would for a somnambulist, stood still, and looked up.
In The Grapes of Wrath, Granma Joad retreats into a somnambulistic state after Granpa's death. She becomes increasingly consumed with her trance-like state before dying during the Joad's' nightlong trek across the California desert.
So, being called a somnambulist might awaken you to what your drama coach really wanted you to hear: Snap out of it!