Who knows? It's only been a week, but a depressed person thinks depressed thoughts and thinks of life as being irrationally sad and hopeless. An anxious person thinks anxious thoughts and has irrational fears. Does that describe you? If it does, what you're feeling is a symptom some people feel, but if you're not, the cause is perhaps something else. Don't know how old you are, but life can get pretty odd sometimes and it will feel different from time to time. The more you think deeply about anything you're doing or feeling, the more questions you'll have about it. That's not a mental illness. But if the normal vicissitudes of life overly scare you or make you feel hopeless, that's not necessarily an untrue belief but it defeats the survival instinct and so is a sign something is off. If this continues, the place to start is your doctor if you are not someone who thinks chronically anxious or depressed thoughts.