"Electromagnetic pulse." He was answering how the power and apparently the phones were knocked out without considering that the explanation probably didn't mean anything to Hiccup. He wasn't sure if it was all Lorna that caused that or if his attempts to hold it back and the backlash of his own loss of power at the end had attributed to it.
The stumble jarred his head which made him grit his teeth and close his eyes and when they were both steady he ended up letting his head drop forward a little and accidentally clonking Hiccup in the side of the head with his forehead. It made him see stars even though it wasn't that hard of a hit so he left their heads leaning together while he recovered.