[verb (plain)] + せいか [i-adj] + せいか [na-adj] + な + せいか [noun] + の + せいか
せいか means "perhaps because": you notice a result and offer a cause you are not sure of. It attaches like せいで – the plain form of a verb or an い-adjective, a な-adjective with な, a noun with の – and the result follows.
The second half is something you observe, not a plan or a request.
きのせい気のせい is "your imagination", so きのせい気のせいか is "maybe it's just me, but".Because せいか only guesses, it also works where the result is neutral or even pleasant, which せいで doesn't.