Sedation is either the state of being relaxed or sleepy because of a drug, or the act of drugging someone with a sedative.
Sedatives are drugs that people take to relax or fall asleep, and sedation has two related meanings. Sedation can be the condition of someone who has taken a sedative. You're in a state of sedation if you're relaxed, mellow, sleepy, or low-key because of a drug. Also, sedation can be the action of doctors or nurses in calming someone through drugs. A nurse may put a patient under sedation if they can't sleep. Sedation is an act of drugging.