"I was under the impression that the psychoactivation from THC would keep you awake."
The effects of taking cannabis can vary widely between varieties and between people. The biochemistry is complicated, and no one cannabinoid like THC or CBD can really be thought of as responsible for a certain effect. THC is usually stimulating by itself, but when accompanied by CBD and other cannabinoids as well as the many terpenoid essential oils found in the plant, the net result can be relaxing or sedating. This is sometimes referred to as the "entourage effect."
It depends on what you smoke. indica helps you relaxe and causes a body high while saliva is more of an active type of cannabis and causes a head high which makes you more active, more awake