The Twilight Zone 1959 053 Twenty Two

"This is Miss Liz Powell. She's a professional dancer, and she's in the hospital, as a result of overwork and nervous fatigue. And at this moment, we have just finished walking with her in a nightmare. In a moment, she'll wake up, and we'll remain at her side. The problem here is that both Miss Powell and you will reach a point where it might be difficult to decide which is reality and which is a nightmare. A problem uncommon, perhaps, but rather peculiar - to The Twilight Zone."