The human body can process only so much of any foreign chemical. It doesn't matter if it is alcohol, illegal drugs or even prescription medicinal drugs: if the body takes more of a chemical than it can take, also known as an overdose, the result can be serious illness or even death. If you recognize these symptoms of an overdose in someone, it is vital to get him to a hospital.
Many drugs affect the neurological systems responsible for such vital and autonomous functions such as breathing. Overdosing on a drug can cause these symptoms to begin to function irregularly, and eventually shut down. The symptoms of this process include abnormal breathing patterns. This can take the form of rapid breathing that resembles hyperventilation, or irregularly spaced breaths. The individual's breathing can also become increasingly shallow until the part of her brain that controls breathing shuts down entirely.
Sweating is actually one of the body's ways of cooling itself down. Evaporation is an endothermic reaction, in that the process absorbs energy. When your body sweats, and the sweat on your skin evaporates, it takes energy out of your body. Heat can be thought of as excess energy, so the process actually works to cool down your body. When the body overdoses on a drug, it throws the biological systems into chaos. Sweating is one way the body tries to deal with the raging biological processes within, making it a significant sign of a drug overdose.
Overdoses have a number of effects on various neurological functions. An increase in blood pressure can cause soft tissue to press on the optic nerves, causing the individual to see spots. A depression of prefrontal lobe function can cause intense confusion. Additionally, the individual might slip into an unconscious stupor from which you cannot arouse him by the usual methods of making loud noises or shaking him. In serious cases, the individual could start having convulsions.
Vomiting, while never a pleasant experience, is the body's way of purging itself of toxins. If something is making you sick, then your body will extricate its current stomach contents. That way, if what is making you sick is something you ingested, it is removed from your system so it can't make you any sicker. Especially in the case of alcohol poisoning, this purging is a sign that someone has overdosed. This purge is especially important in the case of overdoing on alcohol since the body will continue to metabolize the alcohol someone has already consumed, putting even more alcohol into the bloodstream, even after she stops drinking; this metabolizing will continue even after she passes out. Consequently, just because someone has passed out does not mean she will not continue to get even sicker internally.