If histamine makes you feel more awake then that indicates that it is able to function normally as a neurotransmitter and that your immune system is not overstimulated and that your body can clear away this neurotransmitter signal quickly by breaking down the histamine thus be more sensitive to it. However, if levels are very high then histamine, in performing its role in the immune system, will cause excessive increased permeability of blood vessels and low blood pressure, which induces drowsiness.
Histamine has various diverse biological roles in different types of tissue. There are several different types of histamine receptor which can be sensitized or desensitized by various cofactors. Each anti-histamine drug targets a different type of receptor. Hence it's a very complex subject which has not been the focus of much detailed study to date.
My weirdo response is similar to your husband's.