A "range-bound" market could soon swing more dramatically, and an "overshoot" may send stocks 10 percent lower in the coming months, Mohamed El-Erian said Thursday.

"Don't be surprised if you see a 5 to 10 percent move the other way, because that's what we've been having actually for a while now," the Allianz chief economic advisor told CNBC's "Fast Money: Halftime Report."