In my case it was my wife who urged me to retire and I must confess it was a bit of a mental challenge for the first few months as I found I actually missed the intellectual challenge of work and also being around people. However, I do like to keep busy! so this was quickly replaced by the challenge of various major projects that have been on the back burner for years. For example I have a smallholding which keeps me fairly busy, I'm currently building a new timber and stone greenhouse for Mrs J followed by a new workshop. I also take an active part in community projects in our village which provides just enough human interaction! I certainly don't miss getting up at 5:30am to travel to lord knows where every day. Having said that I do know several self-employed people who love their job and have no intention of retiring.I can remember from a pre-retirement workshop that for many it is that step into the unknown, a big change in daily routine and the fact you are entering that 3rd stage but once over that step it can be a great feeling, Mike realised that you have to give up some income to get over this step but quote "I'm far happier in this new stage in my life ".
I can also say the same, and a big part is keeping occupied which can be easy or difficult depending on yourself but most seem to say they do not know how they had time to actually go to work. I know some people who do voluntary work for a few hours a week and others who work part time doing something they really like rather than the job they had but you do need to get to grips with the finances, good financial advice may be helpful. What you don't want to end up doing is having to work for less because you got the sums very badly wrong and only you know your finances. Also don't keep finding excuses to put it off, take a positive approach otherwise you end up chasing a moving target you never reach and so many also get it wrong, wake up one day and realise they have missed any chance of a decent retirement, eg read @Lons post.