There is some pain (similar to being snapped by a rubber band), but according to Kolotkin, "most people find it tolerable."
You can also numb the area beforehand with ice or lidocaine, a cream you get via a dermatologist's prescription. Kolotkin also recommends not scheduling appointments when you are premenstural since you will be more sensitive. Taking Advil beforehand may also help.
While electrolysis will be permanent, it is not a fast fix and requires a few separate, 15-minute-long appointments to get to that step. Hair does not have to be a certain length to start electrolysis, and you can shave in between appointments, but once the process has begun, you must refrain from waxing, tweezing, or threading the area.