Shaun posted an emotional but also hilarious message Tuesday on Facebook announcing he's checked into a long-term rehab center. TMZ broke the story ... Shaun was busted earlier this month for public intoxication. Shaun spent a few hours in the drunk tank and, though he wasn't cited, his arrest did produce this incredibly sad mug shot that had his fans feeling bummed for him.

Shaun wrote, "At this time, in an effort to break free from the self destructive patterns of behavior and drug abuse that have landed me at rock bottom, (to be real... BELOW rock bottom. Even rock bottom is like 'holy sh!t, how'd you get all the way down there?') I have checked in to a well reguarded, long term rehabilitation center. I have surrendered to the reality that without immediate treatment my life is in eminant danger. My spirit was until recently depleted, weak and shrouded by darkness has been renewedby the overwhelming out-pouring of love and support from fans of my early work as an actor."

He went on to thank fans and even loved all the food they were dishing him. He said, "Reaching out to me not only on-line, but in person. Everywhere I go, morning, noon and night, folks whom I've never met before approach me with big smiles and hugs, invigorating encouragement, even food. And not junk, the good stuff, grandma's stuffed peppa's."

"I hear stories about how much Heavyweights or the Ducks movies impacted their lives or helped them through hard times or just made them laugh over and over. Such a testament to all the blood, sweat and tears everybody put into those flicks during that magical time over 20 years ago. Please believe how medicinal these personal exchanges are for me. Even if you think I'm the knuckle-puck guy or the fat kid from 'Hook'. In the midst of my most challenging times your support is giving me the strength I need to embark down the long road to recovery.

Shaun's stand-up continued, because he wrote, "(Self...please, DO NOT type the next line)" before writing this, "Guys, you ARE the wind beneath my wings. (OMG... you went there. A flying V/ Duck refference ON TOP of a throw-back to classic Bette Midler?... you promised you'd be sober when you wrote this...)."

He clearly got a kick outta writing this.

Shaun finished his post, saying, "Losing the privalage to share life with you is heavier than the guilt I must carry. I ask not for forgiveness, not for another chance or keys to your OTHER car. However, in knowing the transformation I'm striving for is beyond my own mind and body, I do seek your prayers. If you will.

"Let me thank a few without whom I'd have already been the subject of the lowest rated E true Hollywood story ever." Shaun thanked family, friends and a nurse at UCLA who helped him proof his post.

Get well, Shaun!!