Lloyds Banking Group boss Antonio Horta-Osorio will return to work today after extreme fatigue forced him to take a two-month leave of absence.
The 47-year-old was in the midst of implementing his strategic vision for the bank last September when he was having trouble sleeping, but it was not until his wife Ana became increasingly worried in November that he sought help.
The Portuguese-born banker, who spent a week in the Priory clinic, admitted he "could not switch off" after he "focused too much on too many details".
Lloyds saw its shares slump when Mr Horta-Osorio stepped down, amid fears his departure could turn permanent and derail progress made with reviving the taxpayer-backed bank.
Lloyds, which is 40.2% state-owned, previously said it completed a rigorous process, including independent medical advice, before deciding its chief executive was fit to return.
The bank has agreed to an initiative from Mr Horta-Osorio which will reduce his direct reporting lines and strengthen the roles of its senior management team.
Mr Horta-Osorio said he realised something was wrong at the beginning of September when he noticed that he had trouble sleeping.
"I'd go to bed exhausted but could not sleep. I could not switch off. I understand now why they use sleep deprivation to torture prisoners," he said.
Group finance director Tim Tookey took over as chief executive.
While Mr Horta-Osorio was away, Lloyds named the Co-operative as its preferred choice to buy 632 branches it is selling under European competition rules. The decision to start exclusive talks with the Co-op did not involve Mr Horta-Osorio.
Lloyds is being forced to divest the branches because of the £20bn in state aid it received following the 2008 financial crisis. The plan is seen as a way of introducing a stronger challenger to the big five banking groups.