A deep and primal yearning that crashes over you in waves. A thorn in your psyche; always a subtle throbbing but impossible to ignore once anything diverts your attention to it. Constant intrusive thoughts, loneliness, frustration, panic, desperation, aggression.

Other people are saying its akin to hunger, but I'd say it's more like thirst. There's a stronger sense of urgency and a subtle feeling that's always present and ready to bubble up to the surface at any moment to override everything else.