Caught Masturbating at Work

I'm married but today, I got so turned on looking at pics on my phone that I started jerking off at my desk. My cock was hard and slick with pre-cum as I pumped myself, groaning quietly into my hand. When I came all over my fingers, shooting thick ropes of cum, I froze in shame until I heard the click of a coworker's pen, they must have walked by just then and seen everything. Am I sick for doing this? Is it normal to be so horny at work?