I don't think anyone would want to give you wrong advice here, so definitely see a doctor as soon as possible. If it can be arranged, it is best to jump right to someone who handles athletes - or at the least an orthopedist. Your typical family doctor will most likely just prescribe rest for a few weeks before passing you along to a specialist. You can probably save some time by skipping that step.
My son went through UCL issues as a freshman. His MRI ended up being inconclusive, and the doctor felt that since a large tear wasn't evident, we should try physical therapy first. That ended up being the correct call as post therapy (and some mechanical changes), my son hasn't had any elbow issues for almost three years.
As for the velocity drop off - One of the things our body will unconsciously do is to protect itself. If you have an acute loss of velocity, there is usually something wrong even if consciously you don't realize it.