If a sufferer is seriously ill or if vomiting has commenced, the pylorus will be constricted, and oral drugs may not reach their site of absorption. The drugs must be administered parenterally. Some agents are suitable for intramuscular injection if an intravenous line is not available. Sufferers severely affected by seasickness should not dive, and they should lie down and try to sleep. A mild degree of sedation is sometimes very helpful if the patient is being supervised by someone suitably qualified. This can often be achieved by use of an antihistamine that is not only antiemetic but also sedating (e.g. cyclizine). Under these circumstances, a drug such as droperidol in very small doses may also be helpful, but there should be no diving if sedating strategies are used. If there is a prolonged period of interrupted oral intake, intravenous fluid and electrolyte replacement may be required; seagoing medical officers have observed that the fluid may be more important than the drug.