I'm wondering about this Irish language song because I was reading in comments to Mudcat thread about Seachrán Charn tSiail that there are legends of fairies taking people around the whole of Ireland in a single night. I suppose that is what Seachrán Sí would be about as seachrán is a word referring to wandering and wanderers and Sí refers to fairies.

also saw this reference on line: Sligo Folk Tales - Google Books Result
https://books.google.co.uk/books?isbn=075096555X
Joe McGowan - 2015 - ‎History
"Bernie had fallen victim to the 'shaughran' or seachran sidhe (fairy wandering). It was an enchantment that caused travellers to lose their way on paths and in fields well known to them. Mischievous fairies were held to be responsible and no one ever came to any harm."