He shared a video from hospital after being attacked while out on his mega hike.
The calm Cooler Than Me hitmaker was airlifted by helicopter for treatment after being bitten by the reptile.
His celeb pals were shocked about the news but in fact only one in 600 rattlesnake bites lead to a fatality.
The 31-year-old posted from Colorado: “Crazy day yesterday! I had just crushed 16 miles and was going for 8 more when I got bit by a baby rattlesnake!
“That venom is no joke! I got to the hospital and got the anti-venom in time. Shout outs to G and Mike from the chopper team and Bo and Cassie and Whitney (my nurses).
“I’ll be here a few days and will not be able to walk for several weeks but enjoying the AC and the nice bed, haven’t had those in a while Hahahaha!”
Mike is attempting to walk 20 miles a day to complete his personal mission but gave friends a fright.
Joe Jonas wrote: “Rest up bro. Glad you are OK.”
Brit Jessie J, a close friend of the American, replied: “You are a real life super hero.”
Speaking ahead of his cross-country mission, Mike said he was “terrified” but also extremely excited at the same time.
“The allure of it is its difficulty, its magnitude and the inevitability of self-growth through the project,” he told Billboard.
“I don’t feel like I’m walking to show people who I am. I’m walking to find out who I’ll become.”
He chose to do the hike as he wanted to “for years and years” – and after losing father Jon in 2017 and pal Aviccii a year later, he took the plunge.
“I feel everyone has a list of things they’d like to do in life and then a list of things they have to do,” he said
“After (the deaths) I realised I couldn’t wait to do these things I had to do on that list.
“I’d been putting the walk off for years and years and years. The time is now.”
He added: “On this walk I have to figure out how to be in love with where I am right now. That would be good and be a skill that would benefit my life ahead.”