Bray Wyatt's dad, Mike Rotunda, is opening up on his constant grief following the late WWE Superstar's tragic death ... saying life without his son has been nothing short of a "nightmare."

Rotunda -- who was famous in his own right as a wrestler for decades, most notably as Irwin R. Schuster -- joined the "Wrasslin Talk with Mayor McCall" podcast to discuss Wyatt (real name Windham Rotunda) ... and, understandably, he's still struggling to come to terms with the loss.

"It's been really hard," Rotunda said. "We miss him every day."

"[My kids] would come with me and stay on the road, wherever I was wrestling ... and it's so hard to wake up out of this nightmare and he's still not there."

Rotunda explained Windham was supposed to get married to his partner, Jojo, recently ... making it an especially challenging time for his family.

Rotunda praised WWE for helping his family by giving Windham a Legends contract among other gestures ... which will allow his four children to receive financial help from merchandise sales.

"He was a jolly fellow," Rotunda continued. "He loved to laugh, he was loud, always laughing and he lit up a room. He lit up the wrestling business. People come up to me and have a story with Windham and say, 'He took the time to sit there and bulls*** with me for 10 or 15 minutes when he's supposed to be signing autographs.' So many people come up and support him by wearing Windham's stuff, and they have a story about him. He was that kind of person."

As we previously reported, Windham -- who experienced heart complications leading up to his death -- passed away while taking a nap at his home in August.

He was just 36 years old.