Eli Lilly has agreed to pay up to $7.8 billion to acquire Centessa Pharmaceuticals and its experimental drug for excessive daytime sleepiness, the company said Tuesday . Centessa is one of several companies working on a new class of drugs to treat narcolepsy, a condition that makes it difficult for people to stay awake during the day. The drugs may also be used to treat other neurological conditions that are accompanied by drowsiness, such as Alzheimer's disease and depression, and possibly