(NEXSTAR) — Mark Sheppard, well known for his roles in “Supernatural,” “Battlestar Galactica,” and more, says he is “humbled once more” after surviving a scary health scare.

In a Saturday Instagram post, Sheppard, 59, wrote that he collapsed in his kitchen Friday while on his way to an appointment.

“Six massive heart attacks later, and being brought back from dead 4 times,” Sheppard said in the post, which include a picture of him laying in a hospital bed. “I apparently had a 100% blockage in my LAD.”

LAD, or left anterior descending artery, is the largest coronary artery, according to Cleveland Clinic. The LAD is the biggest supplier of oxygenated blood to the heart’s lower left ventricle and supplies blood to the septum.

If the LAD is blocked, it can cause what is known as a widowmaker heart attack, which is often fatal, Cleveland Clinic explains.

Men older than 45 and women older than 50 are at an increased risk of experiencing a widowmaker heart attack, according to Cleveland Clinic. Other risk factors include a family history of heart disease, lack of exercise, tobacco use, lack of “enough nutrition,” or other medical conditions.

Sheppard went on to thank his wife Sarah Louise Fudge, the Los Angeles Fire Department, and medical staff at Providence Saint Joseph Medical Center, adding that he “wouldn’t be writing this” post without them.

“My chances of survival were virtually nil,” he wrote. “I feel great. Humbled once more.”

Misha Collins, Sheppard’s “Supernatural” castmate, expressed support in a comment on his Instagram post, writing “Mark! You don’t need to do the most and biggest every time! 6 heart attacks? 2 or 3 would have been impressive enough.”

Collins went on to encourage Sheppard to “heal up.”

Days before being hospitalized, Sheppard posted that he had lost nearly 40 pounds in another Instagram post, writing, “Never felt better.” He also shared in a video posted Tuesday that he was going through a “recovery period,” but didn’t explain any further. In July, Sheppard shared about a “nasty little bout with skin cancer” that left him with an “[eight-inch] wide gash in [his] belly.”

Sheppard appeared in 67 episodes of “Supernatural” as Crowley, according to his IMDb page. He also appeared in multiple episodes of “Doom Patrol,” “Warehouse 13,” “Leverage,” and “Soldier of Fortune, Inc.” His most recent credit is five episodes of “Walker: Independence.”