Irkens can only survive 10 minutes without their PAK (explained fully in Ten Minutes to Doom, an unfinished episode); once it has been removed, a 'Lifeclock' appears in their mind's eye, counting down how much longer their body shell can last. The longer the Irken goes without it, the more incoherent and uncoordinated they become, and it seems to take a lot of willpower for them to muster up any strength or logic in their PAK-less state. As well as containing the Irken's knowledge, the PAK also contains their memories, so Irkens would be unable to get amnesia if they receive head injury.