Time spent using your head space for brooding about the past or what-iffing (worry) about the future is a waste of time. All you end up with is feeling more stressed and more depressed about the extent of your problems. It can interfere with a peaceful nights sleep, make you feel touchy and irritable and out of control. Essentially worry is about the future which has yet to arrive and brooding about the past which is behind you. Even if you could go back you can't change it. It is done and dusted so to speak.
Focusing on the present and living life through the senses can be calming, soothing and empowering. If issues arise then problem solve them. Ask yourself the question 'can I do anything about this issue now'? If the answer is YES then get on with it, work out the steps needed to resolve the problem and progress it. If the answer is NO then let it go. Let it go by leaving the thought alone by disconnecting from it. We have approximately 6,500 thoughts a day and can't possibly engage and overthink them all. Those that cause us trouble, anxiety and change our mood state intentionally just let go. Focus instead on meaningful and purposeful activity. Distract yourself by letting go of bad thoughts and have some fun, laugh out loud and find enjoyment in your day.