Playboy model Katie May literally died at the hands of a chiropractor who had no idea what the hell he was doing and suspiciously tried to hide it ... so claims her estate in a wrongful death lawsuit.
Alex Maimon -- the executor of Katie's estate and father of their 8-year-old daughter, Mia Eden -- is suing Dr. Eric Marc Swartz. In the docs, obtained by TMZ, Maimon says a reasonable chiropractor would never have given Katie the "aggressive neck adjustment" that ultimately caused her death in February 2016.
Ronald Richards, the estate's lawyer, says Swartz should have sent Katie to the hospital for a CT scan instead of treating her ... given the severity of a neck injury she'd suffered during a photo shoot.
TMZ broke the story ... the coroner determined Katie's cause of death stemmed from a chiropractor's adjustment -- a blunt force injury tore her left vertebral artery, and cut off blood flow to her brain.
According to the suit, Swartz wrote Katie's patient report 4 days after she died. Her estate thinks it's fishy he didn't write it immediately, and ... "it begs the question whether Swartz went back to change his report after he was notified May was hospitalized and died because of his treatment."
Katie's estate is suing for malpractice and negligence ... as well as wrongful death.
We've reached out to Swartz's office, but so far no word back.