Presley Gerber's Last Post About Rehab Shows Cindy Crawford, Sister Kaia's Support

Presley Gerber's penultimate Instagram post now reads like a gut punch ... with Cindy Crawford's son saying he hoped a frightening treatment experience would be the last one he'd ever need.

Presley's famous mom, dad, and sister were right there cheering him on in the comments.

Cindy replied, "You are a warrior! Walked thru the fire to find yourself! So proud!" ... with Presley responding, "love you mama!!!"

Kaia Gerber also jumped into the comments, writing, "that's my brother I am so damn proud." Presley replied, "love you so much!"

Rande Gerber praised his son ... "I'm so proud of you and your courage. Facing what's hard takes real strength and watching you find your way back to yourself is everything. I love you so much."

Presley shared the post on March 26 ... opening up about undergoing what he called an "Ibogaine Flood Dose" ... and posting a video of himself at a treatment facility during what he described as a quiet moment before "everything changed."

Ibogaine is a psychoactive drug that is naturally occurring... and some folks use the mind-altering substance as treatment for addiction and PTSD. Ibogaine is illegal in the United States, but it's accessible in Mexico and other countries.

He admitted he was "absolutely terrified" going into the experience ... saying letting go of control did not come easily, but he trusted there was something bigger than him guiding the process.

Presley said he knew why he was there and had finally faced what he'd been running from ... writing that somewhere along the way, he started finding his way back to himself.

He also admitted he hoped he wouldn't have to return, writing, "Praying it's the last time I have to come back. Next time I'd like to choose" ... while thanking the treatment team and the friends he made there.

TMZ broke the story ... Presley died Sunday at a rehab facility. A rep for the family said they are asking for privacy during the "very difficult and painful time."