I was forced into retirement through health problems 15 years ago when I was 42.
In the space of two years prior to me retiring I had gone from a fit active gym bunny to a virtual cripple with raging rheumatoid arthritis. The last 6 months of my working life were spent as an in patient at the Shropshire Orthopaedic Hospital where I actually worked as an engineering officer.
As well as the physical disability I also suffered depression and feelings of worthlessness which were compounded by the deaths of my father and father in law in the same year, two men who had had a huge influence on me. I also lost my fishing partner to a stroke the same year.
You could say I was in a dark place and on several occasions considered ending it all.
However, the human spirit is a very strong force and with the help and support of the NHS staff and my family and friends I came out of that tunnel. Modern drugs and physiotherapy keep the rheumatoid under control and when it does flare up I simply hit the pain killers, get the splints out and go to bed. The mental health issues were a bit more difficult to sort out but a couple of courses of counselling and a dose of happy pills have helped me put things back into perspective and I now realise that compared to many people I'm actually fairly well off.
Fortunately I had a forces pension which paid out early as did my NHS pension, I also had a decent lump sum severance payment which I invested into a couple of buy to let houses so financially I'm reasonably secure.
All of his however does not prepare you for the isolation which retirement can bring, especially at times when the arthritis flares up and I am confined to the house. When we are working we all spend time interacting with other people through the working day, this is not the case when you retire which could be why so many retired people are forum users. In my own case most of my friends are still working, as is my wife, 12 hour shifts in her case, so sometimes if I'm too ill to get out I go several days with no human contact for long periods. Anyone in a similar situation will tell you the same, you have to find something to fill your time. For me it's researching and collecting 'Charlie Romeo Alpha Papa' (as my Mrs describes it) or, 'old and interesting bits and pieces of social history', as I like to think of it; and of course fishing when my mobility allows.
In my opinion if you have the luxury to plan for your retirement as well as looking at the finances you would do well to ensure your social networks are in place and not allow yourself to become isolated.