The meaning of なんか is quite ambiguous. In addition to "like or something" as a filler, I feel that in some situation, it also means "for some reason~I'm not quite sure of the reason". However, their essential meanings could be the same; なんか can be used to make the meaning of a subsequent word vague/softer/etc. This idea could be the same with "like/something/for some reason" in English. I think that 浮かれた気分 is a "passive" merry/buoyant mood. The direct transition of 浮かれた気分 is a "floated mood". Then, at least in Japanese, floated=merry=buoyant. I hope this helps.