Will my 'dubious' medical history jeopardize my plans of teaching English (TEFL) in Thailand?

I am a British citizen who is planning on working as an English teacher in Thailand later this year, hopefully through first acquiring a TEFL qualification on location. I have got a good BSc degree, my grammar is good and I have never been in trouble with the police. What worries me though is that I have had problems in the past - namely a drink problem and a failed suicide attempt in which I took a morphine overdose. I have been dry now for a couple of years, I am no longer on any medication and I consider myself to be fit and healthy. Will my medical past jeopardize my plans? Am I unlikely to be granted the visa required for me to be allowed to work in Thailand? Should I just acquire a TEFL certificate in England before arriving in Bangkok and attempting to blag my way?