Diazepam can be used for insomnia, anxiety relief, acute seizure treatment, and drug withdrawal in rehab. All medications in the same classification are addictive themselves and can be diverted as sedatives used in rape. The drug class is benzodiazepines. Other common medications in the same class are Xanax (alprazolam), Ativan (lorazepam), and Klonopin (clonazepam). There are more, but those are the most popular.
Some are mostly used in anesthesia, like Versed (midazolam). Because they are sedatives, they make you less sensitive to stimuli. However since the effect is non-selective to which type of stimuli, they can make you both ignore something which may be bothering you (traumatic memories for example) as well as things which may be actually important to pay attention to (for example the cars ahead of you swerving to avoid debris).