Harrison pulled the prank after inviting the couple to a dinner party he held with his wife PATTI.
Cynthia recalls, "The room swam and we had no idea what was going on until our laughing hosts enlightened us.
"We piled into George's mini, desperate to get home. The trouble was George had no idea which way up the world was.
"I looked in the mirror and saw my own skeleton. I thought I was in hell. As the drug wore off my first coherent thought was that I didn't want to tamper with my sanity."