After falling behind following a slow start, George Maris and a wonder-strike from Omari Alexander-Salmon overturned Forest's lead.
The visitors hit back before Barnsley regained the lead once more in controversial fashion. A phenomenal strike from Bailey Gooda that crossed the line wasn't awarded only for Jamie Moore to nod home.
But with only seconds remaining Forest - guided by former Tykes defender Steve Chettle - claimed their third and a point.
