Fading country superstar Willie Nelson walked off stage in the middle of a Texas gig

with no explanation, and didn’t return for nearly 20 minutes —

sparking fears for the pot-loving 84-year-old.

When the Red Headed Stranger, who has battled emphysema and pneumonia, reemerged, he appeared “disoriented,” say spies.

The scary incident follows Willie axing several tour dates after falling so ill, a source declared him “at death’s door.”

“Willie’s got a new album, new tour and new pot business,” says a music mole. “That’s a lot of pressure.”