The Bee Gees star is in hospital battling colon and liver cancer and pneumonia, and his family have been advised to remain at his bedside.
The 62-year-old was apparently noting ideas for songs and ambitions he wanted to fulfil - including setting up a charity - just days ago.
"He has kept an antique notebook by his bed to write down lyrics and ideas he has had floating around," a friend told the Sunday Mirror
"He has also expressed a desire to set up a children's charity involving music. It was a 'bucket list' of things he wanted to achieve. But everyone is very worried now.
"His family are taking it hour by hour, praying for a miracle. But with Robin they know never to give up. The past two weeks have been devastating. The one aim Robin had was to be at the Requiem premiere.
"It was his motivation, passion and goal throughout the battle against cancer. His spirit has been shattered since the pneumonia and he has gone visibly downhill. Before he slipped into a coma he was struggling to get out of bed without a wheelchair."
Gibb had been in remission prior to the current setback.
Listen to Robin Gibb's song 'Don't Cry Alone' for the Titanic Requiem below: