BIG WHEEL RYAAN'S CRIPPLING ANXIETY!

HARDEST-workingman-in-Hollywood Ryan Seacrest's head is spinning as he takes over for Pat Sajak on Wheel of Fortune, and sources tell The National ENQUIRER he's resorting to extreme measures to keep the butterflies at bay.

"Ryan tends to bite off more than he can chew," blabs an insider about the jack-of-all-trades, 49, who also hosts American Idol, does a radio show and has a cooking series in the works.

"He's a bundle of nerves right now, but he wanted to be the next Dick Clark and that's what he's become. He's only human, though - and filling Pat Sajak's huge shoes on Wheel of Fortune is a challenge of epic proportions," the spy spills.

Sources snitch he has a long list of tried-and-true ways to stay on top of his game before he starts taping episodes, which begin airing in September.