i wouldnt seek medical attention. i would be scared though, in your situation. i think what you're doing now is perfect. learn about sharks as much as you can, and if you feel comfortable, maybe take a swimimg with sharks class type thing. and instead of thinking about the ocean, why not a relaxing beach? picture you tanning and a hot surfer dude coming a bringing you a piņa colada!
ahhh, see, im relaxing already! just do it slowely, soon you'll be swimming in the ocean again!