One of the things that really caught my attention in the Riders of Berk season 1 finale, We Are Family, was how tired Hiccup looked from the end of the first episode all the way to the end of the second. It makes complete sense. He left for the Isle of Night in the middle of the night without sleeping, then was kidnapped by Alvin and probably didn’t get a chance for even a brief nap on that boat ride. Once on Outcast Island he was too busy trying to plan escape and deal with Mildew to sleep. It’s dawn when he is captured, night again by the time they reach Outcast Island, and dawn again when he finds Toothless and his father and friends come to rescue him.  This means he’s been running off of one night’s worth of sleep for over 24 hours. He’s exhausted. That state of mind probably contributed to his irrational actions at the end.