Hi swim,
When my neurologist did one on me it felt like a needle sticking me. I didn't feel great pain from the electricity being used but slight pain of being stuck. Very doable in my case. You might experience something different. I didn't have flare ups, spread or triggers but I've read those who have.
The test was needed to measure nerve pain responses and what nerves did and didn't do and which ones were affected. The test was performed on my left arm so that might be a difference.
Since then I've had full body spread but not being related to the EMG.
The test is needed so do it.
Best of luck...