Robbie Williams has spoken of the “discomfort” and “panic” he feels when he is approached for photos and autographs by fans.

In a post on Instagram, the pop star said he was able to “mask” the reality that social interactions frighten him.

He also detailed his experience on a recent flight, when he received multiple requests for photos. He said that he was sleep-deprived on the US domestic flight when he was approached by a fan who wrote a “lovely note”, praising his Netflix documentary that detailed his struggles with fame.

“I explained I’d been up since 4.30am, had two hours’ sleep, and wrangled four kids through the airport. I’ve got bags under my eyes and I’m dealing with anxiety,” he said. “I explained that if they came and took a photo with me, my anxiety would spike – because then the whole cabin would start wondering who I am.”

More requests came, with another passenger sending him a note, and another making him feel “obliged” after walking up to him and asking outright for a photo, Williams said.

He said: “Every interaction – with strangers or even people I know well – fills me with discomfort. I mask it well. But social interaction still frightens me. So much so, I didn’t go out for years. And I had to do it without drugs or drink.

“I used to find it impossible. Now I’m … OK-ish. But still crawling inside. Every time a stranger approaches – and they are strangers – I panic.”

Williams said this was “dodgy terrain for a famous person to give context around”, as he felt there was an “unspoken law: as a celebrity, you should be accessible 24/7”.

He added that celebrities were expected to “greet all strangers like you’re the mayor of the best town anyone’s ever visited” and “make sure their wishes are met, whatever they are”, but some people were “fans of fame, not necessarily of me”.

“Now listen – if we cross paths in the wild and you are a fan of me, I want you to tell me,” Williams said. “That means a lot. I’ll make time. I’ve got gratitude for that. It warms my heart when I feel I’ve warmed yours.”

He urged fans to give celebrities the “dignity of their privacy, their wants, their needs”, as he could be “on the phone with my mum, talking around her dementia” or “thinking about my dad’s Parkinson’s”.

Williams, 51, is equal first with the Beatles as the act with the most No 1 albums in the UK, having had 15 chart-topping records. A biopic, Better Man, was released last year, in which he is portrayed with CGI as an anthropomorphic chimpanzee, a comment on how he feels like a “performing monkey”.

The former Take That singer has a well-documented history of depression, as well as being agoraphobic, and has been in rehabilitation in the past for drug and alcohol abuse.