There is security in the present. You know what you have here. It is calming for your mind. But the mind is trained to remember the past and to foresee the future. It is so well-versed in this occupation that it gets uneasy when it has to concentrate on the present. The present is simply boring to the mind. But if you manage to redirect your attention from the stream of thoughts to the presense the mind will have chance to rest, to rest from the hard work of constructing possible scenarios of future happenings or reconstructing the full picture of past events from few, vague memories. The mind is so accustomed to this tasks that it won't stop. So getting it back to the now is a bit hard, it is an effort. It is like breaking a fascinating game for a child. But if you don't teach it to rest in the present it will get completely exhausted and you with it. So for your own good, teach it to rest by being in the safety of solid, physical, present reality. HOW? Learn meditation.