I have heard many people describe what you describe as a symptom of depression for them. It happens sometimes to me but not often. Depression causes a huge loss of concentration for me but not quite to what you say. Some people say they can be that way for an hour or more, just in a catatonic state and not realize it. It doesn't sound like psychosis to me. For me when severely depressed I can tell my brain is so inactive and is just not firing at all like normal.