Professional surfer Kalani David has tragically passed away ... after the former Hawaiian champ suffered a massive seizure while practicing in the waters of Costa Rica.
He was only 24.
The Costa Rica Judicial Investigation Department shed some light on the accident, telling AP News "he was surfing when he apparently suffered some kind of epileptic seizure and drowned."
They added ... "The death is still under investigation."
Legendary surfer, Kelly Slater, paid tribute to David on his Instagram .