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Demaryius Thomas says his violent car crash earlier this year scared the hell of him ... telling TMZ Sports he could have DIED after he flipped his SUV in Denver back in February.

"I could have been gone," the NFL star receiver says.

As we previously reported ... Thomas was doing 70 MPH in a 30 at around 12:20 AM on Feb. 16 when he lost control of his SUV and crashed it into a curb.

A witness says he saw Thomas' car flip several times in the air ... and the pics we obtained from the accident show the gnarly scene.

Thomas says it was a pretty traumatic experience for him ... and tells us he's not only thankful he can still play football -- he's happy to just be a functioning human being.

"I wake up every morning and thank the lord above," Thomas says ... "And, just thankful for just not even just being able to do what I do -- being able to talk, walk, eat, all those things that we forget about on a daily basis."

Thomas -- who signed with the Patriots just a few weeks after the wreck -- is clearly taking advantage of the second chance ... he helped give kids free haircuts and braids at his "Summer Break" event over the weekend.