To quit day dreaming. you much do reality checking i.e where do you stand in your life presently + what are the situational demand + what are the losses you are having because of the day dreaming. Once you are able to do so, you will stop doing that. It will further motivate you to plan accordingly.

A world of fantasy is easy to build and very comforting and can frequently replace reality when it becomes an addiction. Some amount of day dreaming is natural and everyone does it. Excessive of anything is however habit forming and therefore addictive. You are absolutely correct in being concerned, since whiling away time in a fantasy world will mean that real life will pass you by. Remember, your fantasy is self conjured, so will have no negative intonations or experiences. Everything will fall into place just the way you want it since imagination has no limit. We all love to create our own paradise. This is an escape mechanism. Real life will be completely different and by not going out in the world, you are losing out on valuable life lessons which will cause you a lot of difficulties later on.

It's a good sign, that you are seeking  help now. Fix an appointment with a Counselor,  at the earliest,  and understand your inner self.

Hi. Your day dreaming is definitely a result of your inability to focus and concentrate. Difficulty in attention and concentration can occur due to multiple conditions like depression, anxiety or ADHD. You should consider seeking psychiatric consultation and get yourself completely evaluated. Accordingly, treatment can be initiated.