Final answer:
The side effect of Diazemuls among the given options is sedation. Diazepam, the active ingredient in Diazemuls, commonly causes drowsiness and tiredness which is also the intended effect for certain medical procedures.
Step-by-step explanation:
The side effect of Diazemuls (a brand name for intravenous diazepam) mentioned among the provided options is C. sedation. Diazepam is a benzodiazepine used to treat anxiety, seizures, muscle spasms, and sedation during medical procedures. Side effects of benzodiazepines like diazepam commonly include drowsiness, tiredness, and sedation. Therefore, options A (tachycardia), B (hypertension), and D (hyperventilation) are less likely to be side effects of diazepam. It is important to note that while sedation is considered a side effect, it is also the intended therapeutic effect when Diazemuls is used for procedures requiring sedation.