Two possibilities... It could be large enough that the person is aware of a pulsing sensation that keeps him awake. Alternatively, if the aneurysm is thrombosed (clotted), there could be compromised blood flow to the foot which causes pain at night because the leg is elevated (the blood flow is so limited that the person needs the benefit of gravity to get blood to the foot).
It could. Popliteal aneurysms can be very painful and could affect sleep.