Julie, the advice you have been given about not swimming is probasbly a bit over-simplified. Swimming is brilliant exercise for someone with HMS as you are exercising in a medium (water) that provides support as well as resistance, and is no impact. However, like anything with HMS, you need to be aware of what is happening to your body while you are exercising. For some peeps this may mean no breast-stroke kick as this places more stress on the knees, or no butterfly because shouldersare over flexing, and so on. But you don't have to swim a standard stroke anyway, so if breast-stroke arms and dolphin kick suits your body, go for it, or if you can only use your legs, do it that way, and not to do too much of any one thing e.g. all kick work may be too much for your ankles/hips/knees. Running in water is another possibility, as is walking and any other kind of exercise that you can transfer into the water, like cycling your legs or arm exercises using floats for resistance. There is a thread about swimming here
As fatigue is such an issue with FMS, it is really important to start swimming or exercising at a low enough level that your body can cope with, and to increase very slowly. It is really easy to get carried away and do too much when you are in the water as your body is supported, only to have it hit you later on.
Diagnosed HEDS December 1st 2005. DD1 (20) HEDS and scoliosis (now corrected by surgery), diagnosed June 2006. DD2 (18) mild HMS. Son (11) some hypermobile joints, poor muscle strength and seems to be developing scoliosis as well, woopee!