that used to happen to me when i first started smoking..I'd get real slow and tired and feel like wanna sleep but can't... I started drinking energy drinks when I smoked and that helped..put me in a better mood..let me enjoy myself alot longer too

or eat sumthin before you smoke..I know if i haven't eaten anything all day then i sit down with some friends and smoke i lose my high alot quicker than them and normally feel like shit once i come down