"They gave me general anaesthesia and I reacted badly to it."
Neven said during his plastic surgery doctors diagnosed him with the rare condition, priapism, a condition where men suffer painful erection that lasts for several hours.
It's not necessarily related to sexual stimulation or excitement and won't disappear after orgasm.
If the erection lasts longer than four hours, it's deemed a medical emergency.
Permanent damage can be caused if it isn't treated quickly, and can result in a man being unable to get an erection in future.
The condition happens when blood rushes to the penis and is unable to flow out.
Anything that affects the nervous system can trigger priapism.
Disrupting the normal way the nerves that trigger an erection work can widen the arteries in the penis causing more blood to flow in than normal. And lots of different medications can also play a role.
Anticoagulants - used to thin the blood - such as warfarin and heparin, are linked to priapism, according to the NHS, as are drugs used to treat erectile dysfunction, some antidepressants, and drugs used to treat high blood pressure.
In some cases recreational drugs such as cocaine, ecstasy, crystal meth and cannabis have also been found to trigger the nasty condition.
The reality star recovered in hospital, but said doctors there refused to give him painkillers despite him being in agony.
During his stay, he said: "I reside in Belgrade hospital since Friday.
"Unfortunately, I do not get analgesics because they do not give them to patients here, so I continue to suffer.
While he spent some time in London filming with Channel 4, Neven adopted the motto: "Better to hate me because for what I am than to love me for what I'm not."
And he said he's considering more non-surgical treatments to improve his looks such as another "vampire face lift" - where platelets are extracted from a patient's blood and then used as a skin filler.
He shrugged off criticism that his extensive surgeries have worsened his looks.
"I often hear from people that I looked better before surgery," he said.
"It was a long time ago and I'm curious, who will not look better if they are 20 years younger?"