United Kingdom, April 19 -- Robbie Williams has opened up about his struggles with fame.

The 51-year-old singer took to Instagram to share a lengthy post where he explained how fans asking for selfies can cause him discomfort and panic and he shared some examples from a recent flight he took in America.

Robbie wrote: "I'm sat on a domestic flight, going across America.

"I've had three interactions so far with fellow passengers. One of them handed me a lovely note -kind words about my documentary - and then asked for a photo.

"I wrote a note back. I explained I'd been up since 4:30 a.m., had two hours' sleep, and wrangled four kids through the airport. I've got bags under my eyes and I'm dealing with anxiety. I explained that if they c...