There's nothing to be worried about. Every child gets a gene for eye color from each parent. You obviously have the blue-eye gene as one of yours, but because brown is dominant, the brown shows up for you. Your son got your recessive blue gene and a blue gene from his father as well.

I remember the chart from biology class:
B=brown gene
b=blue gene

B b
B b

Each parent has two genes. If they both have brown eyes with a recessive blue gene (Bb), you have a one in four chance of a blue-eyed child. If one parent has blue eyes, and the other brown with a blue recessive gene, you have a 3 in 4 chance.

Often the brown is only "partially dominant," and so a child will end up with light brown eyes - also called hazel or green. You KNOW that person has a blue and a brown gene.

Both my grandfathers had blue eyes, so even through my mothers eyes were very dark brown, she obviously has a recessive blue gene. Dad's eyes are hazel/funny colored we call 'em. And sure enough, just like the chart we drew in biology class, they ended up with four children - two with very dark brown eyes, one with partially dominant brown - so hazel eyes, and one - me - with blue eyes.

Recessive blue eyes has no connection to diseases caused by recessive genes. Genetics is much more complicated than that, and science is learning more every day.