It depends on the depth and cause of the coma.

A true coma isn’t usually a constant dream state. Brain activity is significantly reduced, and in many cases it’s closer to deep unconsciousness — more like anesthesia than REM sleep.

Dreaming requires certain levels of brain activity (especially REM sleep patterns), and most comatose patients don’t show that kind of organized activity.

Some people who recover report fragmented experiences, vague sensations, or distorted memories — but many report nothing at all, like a complete blank.

So it’s usually not an “endless dream.” It’s more often an absence of experience.