Depersonalization/Derealization is what you're experiencing here.
Currently I've had the former for the past two and a half years now due to my cannabis smoking, but for you, you haven't touched it in quite a while, so the only thing I can see that's causing this is stress. Usually Depersonalization is triggered by drinking, smoking (whether it be cigs or tree), or any drug entering your body, it's when there's a chemical imbalance in your brain from said drugs and your brain is trying to process it but can't really, which in turn causes this effect (in the context of drugs).
Now in general, this can be caused by eating worse, being stressed out, anxiety, not enough sleep, a number of those things really. I recommend reading up on it and seeing if it matches the description of what you're feeling.
Onto that, what exactly does it feel like? Does it feel like you're in a dream sorta? Like you're just an observer in your body?