Drop and create stored procedure
The phenomenon is generally known as parameter sniffing. You got a bad execution plan due to an unusual set of parameters, and by dropping and recreating the stored proc, you've just cleared the cached execution plan for that stored procedure.

Related reading material:


Slow in the Application, Fast in SSMS by Erland Sommarskog
Why Is This Query Sometimes Fast and Sometimes Slow by Brent Ozar (uh, me)
How to Start Troubleshooting Parameter Sniffing Issues by Brent Ozar (dang, that guy is good)