Hi,
Your everyday thoughts impact on your dreams. If you're worried about your cat, it will surface in your dreams. However the dreams are created by your subconscious to do certain tasks in the sleep; sometimes to wake you, other times to keep you asleep. Dreams entertain you while you sleep and divert you from external or internal influences that would wake you up.
If you take any medicines, they could make your dreams more vivid. However all dreams are created to help you and do their work while you're asleep. The should be forgotten and disregarded on waking. You're OK.