I really do not think that what you describe in terms of your ailment would have even the slightest bearing on you passing the SIA medical. If you can walk, run, kick a ball you will be alright. Don't forget the medical has nothing to do with SIA but with CAAS.
Your water phobia - should you get in you will have to surmount that problem then - in terms of the SEP training wet drill. It should not present any problems in the interview process, and obviously you would not mention it in any interviews!!
Good luck -