I was driving my 1997 Chevy Suburban the other day and when I pulled up to a stop sign all of the sudden my brakes felt super spongy, like the system totally lost pressure. Before that they had worked totally fine. I checked the fluid and the level was fine, and I couldn't spot any leaks. We did hit a large bump when I was pulling into a parking lot, and I thought maybe something would have dislodged one of the brake lines or something but everything seems fine. When I pump the brakes a bunch, they will kind of hold for a few seconds, but then it slips again. The e-brake works fine to stop the car, but that's not exactly a long term situation.

What's going on and what do I need to do?