Cable Slack

Hey guys,

had a clipless moment last night. Saw a green traffic light and assumed that the traffic would start moving by the time I got to it. It didn't and I didn't leave enough time to clip out.
This caused a lovely slow fall to me left hand side in which the bike (Spesh Secteur) got bashed against the kerb.

Everything seemed *mostly* fine - I had to re-centre my rear brake caliper but that was it.
Since the moment though, I'm having trouble with my rear brake cable. Basically, the cable running under the top tube seems particularly slack, even though the brake pads are almost touching the rims (so, if I try to adjust the cable tension via the barrels they start rubbing the rims). When I pull on my left brake (Shimano 105), the brake engages and cable becomes tight. As I let the shifter go, it seems to put even more slack in the cable for about 10 secs or so, during which time the shifter moves 'freely', i.e. if you immediately pull the lever, it will move around 45 degrees instantly before starting to tighten the cable and engage the brakes.

Could this be something do with the cable getting a jolt at the shifter end during the fall? It always seems to be my damn shifters that get knocked when I have these moments....

Thanks