Married mother-of-one Dr Jean Paton-Ker, 41, secretly met the man in a pub after a flurry of text messages before going home with him for sex.
The patient, then 40, was suffering from depression after splitting with his girlfriend and the GP had increased his dosage of anti-depressants to combat his low moods.
Dr Paton-Ker also gave the patient her mobile phone number because she was scared he would commit suicide and he then texted to say he was attracted to her.
After a flurry of text messages over a couple of months, she met him in a pub and went home with him for sex, the General Medical Council (GMC) tribunal heard.
The fling was exposed when her husband, a gastroenterologist, when he found incriminating texts about the sexual liason and threatened to report her to the GMC.
After the breakdown of her marriage, she reported herself to the GMC and today apologised to Patient A as she begged the tribunal to let her continue as a GP.
She said: 'I decided to meet him because I think I recognised there was some level of mutual attraction. When we met in a pub it was a weekend and it didn't seem like a doctor/patient scenario - it felt like two adults meeting, although I accept now that it is not how it was.
'Afterwards I immediately realised I had done something completely outside what I should do as a doctor and felt really shocked about my behaviour. I've never done anything remotely like that before or since. I accept responsibility for my actions absolutely.
'I had things going on but this was ultimately my responsibility to act as a professional and I didn't do that. I was just ashamed of my behaviour and really wanted to understand how I could have got myself in that position where I behaved so unprofessionally. I've not had the opportunity to apologise but I do.'
The hearing continues.