I will start by asking what you call lunging?
To me running around at the end of a rope is not really lunging.
I have been taught how to use side reins. It is people who injure horses with side reins, not side reins.
As to your question. The number one rule is of course safety first. A lunging cavesson has the lunge rope at the nose. This gives you more control as you have a lever in front of the horse to pull from.
When lunging you should always wear gloves and a helmet.
If the horse really explodes and she said it did and that she could not hold the horse well then you have to let go. You are outweighed.
My boy did this recently as I went away and left him with a round bale, (as I felt I couldn’t leave the rescue horse with just grass) He ate much more than I imagined and was now in the realm of overfed and overworked. Experience tells me that it took him 2 weeks to get to that stage so it will take 2 weeks to come down from that stage.
I was lunging him when he exploded. He knew exactly what he was doing and I couldn’t hold him. At the moment I have to lunge in a 50 acre paddock, so physically with side reins and the lunge rein on the front of the cavesson he went and I had to let him go.
WELL he didn’t think that through did he? 10 minutes on the lunge is equal to an hour of lunging and he was galloping full tilt around the 50 acres paddock in side reins. An ex-racehorse.
He went around 6 times before, as he was the furthest from me, I called out aaannnndddd trrrrooooot and when he next came past me I called it out again and he trotted and then halted.
I put him straight back on the lunge and he went around like a lamb.
His mouth was a little sore for the next couple of days, which I was very mindful of. He hasn’t done it again… yet!!
It did take him about a week to get back to normal from being overfed and underworked.