Kevin Hart is back home and can't believe he's alive

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Kevin Hart has checked out of his in-patient rehab facility and is back home where he's receiving intensive physical therapy, but the big takeaway ... he's "grateful" and "shocked" he's alive.

Sources very close to Kevin tells TMZ, he's looked at the photos of the car crash and can't believe anyone walked out alive.

The comedian messed up his back -- 3 spinal fractures that required fusion. He spent 10 days in the hospital under heavy pain meds and was then transferred to the in-patient facility, but he's home now.

He has a physical therapist coming to his house most days ... and he's doing lots of stretching and exercises with therapy bands. He's still in a lot of pain but says he's handling it without all the meds.