You have to think about how WPA works to really let this number soak in. Each team starts at .500 to win, at the outset. If you put together a win, that means .500 worth of points is available to split among all your participants that day, batters and pitchers together, which brings the sum to 1.000 for the complete win. The reverse point system goes for the losing team, accumulating their negative .500 to bring their sum to .000 and the loss.
Pagan in those three batters did more than a typical loss's worth of damage. He turned a very likely win to a very likely loss, in that short span of time. Not unheard of (Cimber had a -.754 just yesterday for Toronto, and we all LOLed), but it's still remarkable.
Pagan's ERA for the season rose from 3.76 to 4.61 with this one game. That's the nature of being a short reliever. Bad as the ERA is, his season WPA is now -.781, worst on the staff, and that to me says more. It lines up better with how much of a gut punch his 3 biggest failures this season have been. He racks up tiny positive WPA in the low-leverage successes, but more than offsets them with these disasters.