Every person goes through a phase of the day thinking about themselves and their surroundings. Yes it's necessary to think and realize the present which let you plan next move. But over thinking make no sense.
Suppose you're in a worst situation, feeling down and start thinking about next days, how you will face. But thinking for future will not change your present, better you start doing good things which will eventually bring good in life. Similarly if you're in good and start thinking about good future ahead, expectations born and when you not get those expectations, you will feel low again.
So my opinion just go with time, time is everything. Good and bad both should be exist in our life so we can taste everything and value it.