Sudden loss of ranking for a keyword

Morning to all,

apologies if this might be the most stupid question of the day, but still I'm going to ask it :),

yesterday I was still ranking on page 2 for a few keywords in G, and since today: bam, they are just are out of the ranking, not on page 10, 20 or 100, just nowhere. My site is still indexed, some other keywords are still ranking ok, except from that few ones that disappeared. I didn't do anything unethical at all. Could please, please anybody help me out with an explanation or…

Sudden loss of ranking for a keyword