From the OED: “1. a. An ovate fruit with a pale yellow rind, and an acid juice. Largely used for making a beverage and for flavouring. The juice yields citric acid; the rind yields oil or essence of lemons, used in cookery and perfumery.”
…the quietly tortured opener of Radiohead’s fourth album, Kid A: “Yesterday I woke up sucking a lemon.” “Lots of people say that song is gibberish,” Yorke says irritably. “It’s not. It’s totally about that” — the mute, vengeful paralysis he felt in Birmingham, which stayed with Yorke deep into the strange, simultaneous recording of Radiohead’s twin hits, Kid A and the just-released Amnesiac.In England, Yorke explains, “sucking a lemon” refers to “the face you pull because a lemon is so tart.” He twists his sharp features into a ferocious grimace.
“That’s the face I had for three years.”
–quoted from RS