The 43-year-old cancelled the last two dates of the European leg of his in September due to 'illness', but didn't reveal any more details at the time.
Now he's said that he fell ill due to 'brain abnormalities' that left him 'dribbling' and with a 'numb' arm.
He started experiencing the symptoms before one of his shows, but still went ahead with it because a doctor cleared him to perform.
After the show he still wasn't feeling well, and had to return to the UK for emergency tests, where doctors found what looked like blood in his brain.
'I had a headache and I was also having trouble breathing. I couldn't get a full breath. After the show, my arm was still numb and my mouth was still dribbling,' he told The Sun.
'I had blood tests done, and I had various scans including ones of my heart and my brain, and there were some abnormalities found, including something on my brain that looked like blood.'
After that, he was taken straight to the ICU but to make the situation worse, his wife Ayda was in the US with his two children, so she couldn't see him.
'I was confused and scared, but I knew I was in the right place. And, maybe naively, I felt like I knew I was going to be OK,' he said.
After a week in intensive care, the Angels singer was allowed to leave but told that he couldn't do anything stressful for a few weeks.
Describing the experience as a 'real scare', Robbie says it's made him start to look after his mind and body better, and he now does yoga and Pilates, and regularly mediates.
'The whole experience gave me a real scare, because I've been in some dark places before but back then I was 23, or I was 27, or I was 32.
'Once you've been on the planet for 43 years, you realise that, even if you've got everything that I have, you're not invincible,' he said.