Dear I’m Meh about life~
Welcome to the Forum, I can imagine it would have been a struggle to post here and I think it was a good move, other peoples experience and perspective can be a lot of help.
First off I'd like to say I'm very glad you like surfing and can do it for long periods. Having at least one thing that is worth looking forward to is a great thing. Do you have any idea why it is so attractive?
Having had suicidal depression for such a large part of your life is an enormous thing to try and recover from, and while it is good you have been to a medical professional and taken meds which have helped that does not mean everything has gone away. In other words it may only be a partial remedy.
Felling lifeless, unmotivated and numb , not being bothered to do thing, is how I felt when depression had a good grip on me. I was probably in very different circumstances to you but was suicidal too. In time things improved. I'd left things for far too long, and that made treatment harder and longer, but eventually those feelings you describe, as well as the suicidal thoughts all lessened to the extent I now lead a pretty good life, with accomplishment, occupation and love.
May I suggest you return to your doctor and talk about how you are feeling and what you are doing. It may well be that your treatment is not as effective as it could be and may need adjusting?
What do you think?