According to the Merriam-Webster, "hebetude" is defined as a state of lethargy and dullness. The connotation of it really goes deeper than that, though. It's that special sort of lethargy you feel when your ass is glued to the sofa, and you know that you need to get up, and that you would enjoy doing whatever it is that you need to get up for, but you just still can't break through that inertia barrier and actually *get* up. There's even an awesome adjective form -- hebetudinous. :D