Ryan Seacrest better hit the gym if "Wheel of Fortune" contestants keep pouncing on him ... 'cause one of 'em knocked him down on his ass while celebrating!

Here's how it all went down ... contestant Daniel Thomas was trying to solve a 7-letter word on Tuesday night's episode to win $40,000 during the show's bonus round.

Ryan kicked things off with the standard offering -- "R, S, T, L, N, E" -- in the "Living Things" category with "S" and "E' appearing on the big board.

Thomas picked “H, G, D, O,” but only the letter “G” came up on the board -- but with just 10 seconds to toss out a guess, Thomas improbably nailed the answer: “Guppies.”

Ryan shouted, “Yes, you did it," and got so excited he opened his arms, inviting Thomas in for a hug, and as they twirled around ... that's when everything went awry.

Check out video -- which is going viral on X -- Ryan celebrates with Thomas, trips and falls on his butt. Luckily, Ryan wasn't injured and was helped to his feet by Thomas.

"Wheel Of Fortune" announcer Jim Thornton made it official that Thomas had secured the $40,000, putting his total winnings for the show at $71,950.

After the announcement, Ryan gave Thomas another hug, but this time he stayed upright.

All's well that ends well.