Is anthrax always severe, or are there people who get mild or slight cases (and get well without ever knowing about anthrax)?

Not always severe: Anthrax can affect only the skin, usually from contact with an infected animal or contaminated soil. These spots are often single, crusted, black, and may ooze. Inhaled anthrax can affect or infect the lungs and is much more serious and can be life-threatening.

Dangerous: No anthrax infection is mild although skin infections generally have good outcomes. Inhalation anthrax is fatal in almost 50% of cases. Without effective treatment almost everyone will have severe disease.

Conceivable: While anthrax is a serious condition, it is very possible that milder cases are never detected. The same applies to any infection. We don't normally look for the cause of mild respiratory illnesses and casually refer to them as walking pneumonia or simply "a cold".

Three types: Cutaneous, gastrointestinal and pulmonary are the three types in order of increasing deadliness. Skin lesions are the least serious and may heal, however, i would not wait for that as effective treatments are available. Even mild cases cause rather bad skin ulcers.