One reason why people find it difficult to practice Mindfulness and stay in the present moment is that they don’t understand that their thinking changes in a low mood. It's important never to believe your own thoughts when you are in a low mood otherwise you will frighten yourself with your own negative thinking/imagination. Watch how when the low mood passes your thinking suddenly becomes better. You will come to understand that
thoughts are not real if they can change with your mood. To quote Shakespeare “There’s nothing good or bad but thinking makes it so”.