This sense of loss may be real or imagined. Simple things like not eating properly and not getting proper rest can cause depression. A reaction to certain drugs can affect a person's moods. All drugs affect the body and the mental processes in some way. If a drug results in the brain or nervous system toxicity, extreme depression could be the result.
Toxic depression results when a person takes too much of a drug or sedative over an extended time.
This kind of depression and drug toxicity will clear up in a day or so after the drug is no longer in the system. If you become depressed while taking a medication consult your medical doctor. Others such as glandular disorders, low thyroid, hyperthyroidism, excessive ovarian hormonal irregularities can cause depression. Repressed anger turned inward upon oneself will lead to depression. Reactive depression, or grief reaction, occurs after the loss of a loved one, job or some important opportunity is very common.