I compare it to when I was a kid, and I didn't want to stop playing outside to go inside and use the restroom... The urge would build up over time, like an hour, then it would get to the breaking point, and I'd be doing the "Pee Pee Dance". It's like that EXCEPT it hits me in a few minutes, instead of slowly over an hour. It's like 1 minute I'm fine, then a few minutes later, I feel like I'm going to burst.
If I'm very near a bathroom, I can make it. But if I'm out in public somewhere, or on a road trip, the urge or spasm, becomes so strong that I start leaking, no matter how hard I'm trying to hold it. When it first started, I had more "Lead time" warning, and I could get by with wearing Depends Real Fit pull-up underwear. However, over the past few months, it's gotten to the point that if I'm not going to be near a toilet, I have to wear a diaper, which has more absorbency.