A member of the Army, Navy, Air Force, or Marine Corps, on active duty who is absent from his regular duties for a continuous period of more than one day because of disease that is directly caused by and immediately follows his intemperate use of alcoholic liquor or habit-forming drugs is not entitled to pay for the period of that absence. However, a member whose pay is forfeited for more than one month is entitled to $5 for personal expenses for each full month that his pay is forfeited. Determinations of periods and causes of absence under this section shall be made as prescribed by the Secretary concerned, and are final.