JD is completely correct. Whatever builds up in your daily life will reflect into your dreaming life. For example: I've had this dentist appointment ahead of me for a long time now and I've been constantly putting it off. It's something that's been bothering me and I've been worrying about (paying for it, actually getting the procedure done-wisdom teeth removal-, and so on) and eventually that can work it's way into my dreams.

That's why it's good to just relax during the day but always keep lucid dreaming/reality checks near your thoughts. Eventually, if for no other reason than a build up of ideas, they will make their way into your dreams.