Speaking for UK.
You will be asked to fill in a questionnaire that includes any previous mental health issues. If you omit a history of self harm and are then found to have lied during the process you will be in a very sticky situation and the process of retrieving that position and achieving a class 1 medical will be challenging and arduous and may well not be successful.
If you are open and honest then you will have to jump through some hoops but you will have started off on the best footing by demonstrating your honesty and integrity and willingness to cooperate with the system.
You will be required to strip to your underwear for a class 1 medical. Any AME will notice any attempt to cover up scars. You're highly unlikely to get away with it and you should not try.
Be yourself. Be Honest. If you're well now then go in there and demonstrate that!
The best thing you can do to demonstrate that you've recovered from this episode is acknowledge it and not make a big deal of it.
Best of luck!!!
OH