The slurring was probably because of the opiates. Put yourself in an environment where you don't have to worry about looking retarded. The people around you will play a big role in your trip. You want your close friends around. People you can trust that won't try to screw with you while you're tripping. I don't think you want to be trying to act sober. You just need to relax and let it take you where it wants to go. If you start feeling weird in a bad way change something like the music or go outside and look at the stars or take a walk through some trees or go to a different room. Keep things mellow and remember that acid is a beautiful thing.

As for the drug test thing, I don't think acid is commonly tested for on most tests. I think the most common things are pot, cocaine, opiates, and amphetamines.