Video footage of the performance, which took place last week on board the Holland America Eurodam in the Caribbean, show Fisher slurring a couple off-key songs, reported TMZ.
There were reports that Fisher, who was featured on the cruise as a "surprise" celebrity guest, was wasted at the time of the show... But her representative said the on-stage breakdown was caused by her bipolar disorder.
"There was a medical incident related to Carrie Fisher's bipolar disorder. She went to the hospital briefly to adjust her medication and is feeling much better now," said her representative.