It was Yule, a time when the old year ended and the new one began. It is also a time when supernatural beings were likely to appear; rather like Samhain (Hallowe'en). The bragarful is a toast drunk between the one to the Aesir and the one to the dead. One is expected at this occasion to utter a boast or make a vow. Hedin vowed that he would have his brother's wife in the New Year. Of course, such a vow would have to be fulfilled but Hedin was so ashamed he left town immediately to look for his brother and tell him what happened.
Astonishingly, Helgi was not angry. He told his brother that the troll woman must have been his fylgjur (??!!) and that he was about to die. He told Hedin that he had his blessing to marry Svava. Then he went to a battle and died. Svava and Helgi were reincarnated as Sigrun and Helgi.
I have several thoughts. First is that the old troll woman might have been an early version of the 'loathly lady'. Hedin should have let her have her way with him. Second, if she is Helgi's fylgjur, why is she appearing to Hedin and causing trouble? Third, this bragarful sounds a little like a New Year's Resolution. The Vikings don't get credit for this little nuisance. They probably should. Fourth, if Svava is a Valkyrie, then she is Odin's handmaiden and has duties. How does she get to marry a human and have children with him? I am working on that last question - what exactly was a valkyrie anyway?