Scott Disick thought he had contracted Covid-19 earlier this year - however blood tests found he has extremely low testosterone levels.
During Thursday's episode of “Keeping Up with the Kardashians”, Kourtney Kardashian's ex-partner - with whom she has kids Mason, 10, Penelope, eight, and Reign, five - revealed his energy levels were depleted so much he struggled to get out of bed in the morning.
Scott - who was dating Sofia Richie at the time - said: "Lately, I've just had no energy to do anything.
"I wake up and I'm just shot.
"I don't have the drive to get up and run around with my girlfriend and my kids.
"I just don't have the energy. I don't know if I'm getting old or I'm just not in great shape, but I just want to see if there's anything wrong with me."
The 37-year-old reality star then decided to go and get blood tests to find out exactly what was causing his extreme fatigue on the advice of Kim Kardashian West.
He said: "I'm definitely a drop nervous to do all these blood panels, because I've put this vessel through a lot of trauma, I'm not going to lie.
"I'm definitely scared, but if there's anything wrong with me, whatever is the best way to get my body functioning better is what I'm going to do."
Scott has battled with alcohol abuse in the past and been through the trauma of losing his parents.
He'd previously checked into rehab twice in 2015, while in April he attended a Colorado facility to "work on his past traumas".
Scott believes that the "bad beatings" his body has taken over the years contributed to his low testosterone.
He continued: "I feel like there's definitely been some stress in my life.
"Missing my parents, it's really hard. My life hasn't always been easy - I used to drink and party and go out a ton, so my body, it's been through some rough waters and taken some pretty bad beatings. I never thought that there was a possibility any of that stuff could affect me in the long run."
Scott went for further tests with a nutritionist and is building his testosterone levels through his diet and supplements.
He added: "I'm very thankful that there was nothing serious.
"It could be from a number of reasons, so my doctor suggested I meet with a nutritionist, who did a more detailed blood test to find out why my testosterone is so low and to see exactly what's working and what's not working on my body."