Q: Horn stays on

On a rainy morning, while driving to work on the highway, my horn turned on and stayed on. I pressed my horn on the steering wheel but it did not help. It started off as just one "beep" and I thought it was a vehicle beside or behind me. Then I heard another "beep" and realized it was my vehicle. The third time it beeped it stayed on for a minute or two and stopped. A minute later it did the same thing and then stayed on which made me get off at the next exit and pull over at the gas station. I turned the ignition off and the horn still stayed on! At this point I grabbed my owners manual to try and locate the fuse so I can pull it out atleast so I could continue on my drive to work. While looking through the manual the horn just stopped and turned off. I still pulled the fuse. I then noticed the fuse had blown. What could cause this issue?

My car has 70000 miles.
My car has an automatic transmission.