Handling Fear

How do you handle fear effects when fear effects part of the party but not the rest?

Do characters run off at different speeds and if so, how do you manage that? Do they go randomly? Do they move at combat speeds or exploration speeds?  What if someone runs without a light? Do they stop to light a torch? 

Since most fear effects last 'Turns', it seems impossible to avoid running over the whole dungeon.

I've had this happen. Characters run at whatever their running speed is, even if it's very different from others (I don't need to be the fastest, just faster than you!). Running through the dark is exceedingly hazardous - see Chases in the Dungeon on pg. 100 of ACKS core - as characters can easily run into things and/or fall down when they can see, nevermind when they're basically blind. For decisions around direction (e.g., left or right?), I've done both random and allowing PCs to decide; it has really just depended on circumstance. In the dark, it would certainly be random (after falling from running into a wall). In one particular instance I've had, a Mage ended up completely separated from the rest of the group (see here: http://www1.autarch.co/comment/22887#comment-22887 ). He was fortunate enough to have cast Light on his own finger, otherwise he almost certainly would've become lunch to some wandering monster. As it was, he had to work his way back based on hasty room descriptions provided during his Fear-induced flight. Fear-effects are really lethal for low-level PCs