The spell dimension door is a very powerful spell. Not only are its effects enormous, but the results of miscasting this very erratic spell. It rips a hole into the fabric of time and space, creating a portal. This rift in reality allows travel from one point, the casting point, to various places, mostly out through other such rifts. This spell takes a great amount of concentration and effort, and can go very wrong. Due to the nature of space and time and the upsetting of balances this spell can cause, the caster can sometimes be inflicted, overpowering his casting ability, making him useless for a short time. Also, opening rifts may allow things through them into this world, things that should not be here for many good reasons. . .