From Wikipedia (which links to various useful articles, if you don't trust wikipedia): "Dissociation is most commonly experienced as a subjective perception of one's consciousness being detached from one's emotions, body and/or immediate surroundings" aka, the person feels like they're separate from their emotions/body/environment. so if by 'numbing and spacing out' you mean like you detach from the world or your body in some way it could be disassociation. You will probably able to tell if it happens to you, the feeling is very different from just spacing out. I don't think disassociating occasionally constitutes a disassociating disorder though, disassociating by itself is a universal human coping mechanism. Like all disorders it has to be extreme enough to negatively impact your functioning. Hope I helped
(Btw I'm not an expert, I'm just summarizing what I know from my psych classes and online searches.)