Hi & welcome'I still feel that at my age I should know better and should be able to get out of it myself.'
Yeah, the voice telling you that is probably depression and perhaps anxiety and low self esteem screwing with you.
Getting stressed in a high pressure job is really bad for anyone, sounds like you made the right decision to leave. That time consuming commute sounds terribly unhealthy too, got to look after yourself mate. Do you think part of the stress at the idea of going back to work is because part of your brain remembers how bad it got at the last place? That would be perfectly normal, the old subconscious tends to override our minds when it thinks we are doing something dangerous.
A huge proportion of GP appointments are for mental health issues. 1/3 of sicknotes issued in the UK are for mental health issues. In our society these issues seem to be becoming the norm. Why not try writing down your symptoms, how long you have had them and how it affects your life. Showing that to the GP will help them understand.
If you are not keen on help from a GP or the counselling / therapy he could refer you for then I can recommend a few things. The best self help book out there is The Feeling Good Handbook by David Burns. I recommended other books and all sorts of other helpful stuff in the following posts.viewtopic.php?f=6&t=30615viewtopic.php?f=6&t=30617
There is loads more good advice on this site, take a look around!