Thanks everyone for the advice, I've got a heartrate monitor to make a start and i've just been doing some walking and i went on the bike in the gym as well, wasn't too bad.
s
The issue is more about changing your lifestyle long term (forever) and less about the extreme things that may or may not happen related to exercise.
You do not jump into a bath of hot water you test it first, and you should treat exercise the same way.
Changing lifestyle is the hardest thing to do it is even more difficult than changing a diet of a lifetime. Very few people % wise stick to an exercise regime involving a gym and for a lot of those who do they do do it to support another physical interest that they indulge in. I say "indulge in" because they enjoy or are totally infatuated and their whole social life spins around this activity and they do gym work because the want to do well at the other.
What you really have to do is find an activity that you can do for a lifetime that comes with friends that you can grow to like and if you can't get to do that activity often enough for the full exercise value of it then you HAVE A REASON TO GO TO THE GYM.
There are thousands of opportunities out there but as an example.you could join a bush-walking club that grades their walks and only has easy walks once per month. The easy walks are something to look forward to and the gym can get you fitter to do their more difficult walks. The more walks you go on the more friends you make and your lifestyle change is permanent enjoyable and healthy.
If you can't find a suitable group you can start one -there are lots of people out there who are stuck in a lifestyle they are not really enjoying too.
You could start by forming a shopping centre walking group and build all the way to do major trekking holidays or find your own ideal level of participation.. As I said there are thousands of opportunities find one that appeals to you and give it a try, if it does not work for you try another. If you have good hand eye coordination there are lots of organized sports and if you don't then the interest can be taken up with the social aspects and being out there indulging in the wonders of nature.
Your focus should be on changing lifestyle and the gym should only be to support that lifestyle, most people do not keep up with their gym sessions for a lifetime. By all means use the gym to get fit but becoming a gym junky is not normally achievable for the majority.