The Cause of the Recounting of Mongán's Frenzy

Mongán's wife, Findtigernd, entreated Mongán to recount his journey to her. He requested from her a period [of delay] of seven years. So it was done. Then that time came for him. There was [then] a great assembly of the men of Ireland in Uisnech in Meath in the year of the death of Ciaráen son of the carpenter and the wounding of Tuathal Máel Garb and the taking of the kingship by Diarmait. The hosts were upon [the mound of] Uisnech. A great hail-shower assailed them there. Its size was such that the one shower made twelve chief streams of Ireland from then until Judgement Day. Mongán rose with his seven men and went from the precinct of the mound together with his wife and his reciter of lore, Caithide son of Marcáen. They saw an excellent dwelling rimmed by trees. They go to it. They went to the rampart. They went into the wonderful chamber there. There was glittering bronze on the house. There delightful open balconies upon its windows. There were seven distinguished persons there. They were providing wonderful things in the house, featherbeds, and coverlets and remarkable jewels. Seven vats of wine were there. Welcome is given to Mongán in the house. He remained there. He took intoxicating drink. It was then that Mongán sang the "Supernatural Utterance" to his wife there since he had promised he would tell her something of his journey. It seems to them it was not very long that they were in the house. It was not the extent of but one night to them. They were there about a year in the house. when they awoke, they saw it was Rath Mór in Mag Léna in which they were. 

SOURCE:
V. Hull, "An incomplete version of the Imram Brain and four stories concerning Mongan" ZCP vol. 18, 1930, 409-419