Mipsy, do it! Riding is such a great sport for relaxation and stress/anxiety relief, the combination of being outdoors, with the wonderful animals of course and the calm relaxed confidence you need to ride well, nothing's quite like it
. Great for children too, teaches them all sorts of skills like the value of hard work, patience, persistence and leadership skills too, as well as being good hearty fresh air'd exercise...
I'd say it's not quite like riding a bike, riding uses a particular set of muscles not common in other sports (doing lots of yoga and pilates can help though), so I wouldn't be surprised/off-put if you find it quite hard work and get out of puff quickly the first few times. It tends to come back quite quickly if you can have regular lessons though - also don't be worried if your bottle/confidence feels like it's gone a bit compared to when you were last riding, no-one is ever as brave/foolhardy as when they are a teenager, often it's a gradual process if you continue riding into adulthood, as you accumulate responsibilities the prospect of falls and injuries does gradually start to be more worrying, it's perfectly normal and can actually make you a better, more careful and thoughtful rider, but just wouldn't want you to panic if you get a sudden wave of fear the first time you get back on!
Re finding a riding school, I'd recommend looking up which schools in your area are BHS approved (I know there are perfectly good schools which don't go for the certification for various reasons but for me the BHS is still your best guide). Don't be afraid to visit and try out several, for me I like to find a happy medium between a place which is too small and only has a limited range of teachers and horses, and one which is too big, swish and impersonal and you are just treated as a number (at one place I rode at for a few months none of the teachers ever bothered to ask or use my name, it was all 'you over there on "Polo", keep your heels down', and I never had the same teacher twice, pretty poor form IMO). Use your instinct and find a place which feels right, has happy, mucky children, staff and ponies around the place and makes lessons fun as well as instructional, that's your happy spot 
Good luck and happy to answer any questions?