You can check out photos or watch a trailer, but I think this review does an outstanding job of describing the disturbing experience. Here's how it starts:
On arrival, the creator and lead performer Jack Aldisert asked if there was anything I'd like to know in advance. Nothing came to mind, so he noted that if I wanted the show to end for any reason, I could say "I want to stop," at any moment. This was sufficiently important that he asked me to repeat it out loud. He also explained that there'd be a short intermission where he'd come out of character to see how I was feeling.
The show took place in a small room made even smaller by a thick curtain dividing it in half. I sat down on one side and instructed to walk through the curtain to the other side when the music stopped. Someone slid an envelope through the bottom of the curtain; it contained a single page formatted like a script. Almost all of the lines were squiggles except for an exchange in which a nurse got a patient's name wrong.
When I walked through, a nurse greeted me with the wrong name, just as the script indicated. I knew I wasn't meant to be roleplaying as anyone but myself, but it still felt odd wanting to perform as a good patient. She took down various personal details, a perfectly familiar scenario made gradually more eerie by:
1. The script
2. The nurse's questions about a clock I couldn't see
3. Her gradually increasing distress that I couldn't recall my nightmares in detail
Before guiding me through the curtain once more, she urged me not to tell Dr. Ligotti I couldn't remember my nightmares, The doctor (played by Jack, now wearing a lab coat) asked me about my nightmares. After some back and forth about the non-existent clock and the nature of knowing whether we're dreaming or not (inability to read writing, clocks, etc.), I agreed to his experimental treatment, which required putting on a sleep mask and wireless headphones.
His review goes into detail as to the rest of the experience, which only gets stranger and stranger. The second half of the post also reviews a Star Trek-themed experience, and his older reviews describe several other immersive experiences.
(The description of The Manikins actually reminds me of the STTNG episode Frame of Mind, when Riker can't tell if he's acting in a play, or having a psychotic episode.)
