moods, thoughts, pleasant and unpleasant

Sitting in my veranda, I watch the thousands of yellow coloured butterflies that suddenly appeared from the nearby tree and are now flitting across the sunlit garden in front. The lawn and bushes are emerald green, now dotted with the yellow fluttering spots. Hanging heliconias decorate the background.
A disturbing image pops up in my mind and spoils entirely the pleasant mood. It is gloomy. A series of disturbing thoughts in a chain pass through the mind, connecting one with the other. I try to ward off the unwanted thoughts by bringing in some pleasant thoughts. The attempt seemed to succeed for a minute, but the mind soon lapses into the uncomfortable, because the ‘problem’ that first brought them lingered unsolved by the side, waiting for an opportunity to jump into any gap that might arise in the process of thought.
When the mind is calm, it seems to be an opportunity for any disturbing image to erupt in any vacant space in the mind. The disturbing images have dominance over pleasant images. Pleasant images have to be invited to the mind and deliberately retained unless they are extraordinarily strong and powerful to sustain by themselves. Even then their sustenance is never continuous. But the unpleasant ones pushes themselves in uninvited and stays put until the connected mood is exhausted.
Image creates and establishes the mood, and the mood creates thoughts, thoughts in turn reinforce the mood and the vicious circle goes on.There seems no other alternative but to stay with the bad mood, observe and study closely its behavior without letting the mood create images and thoughts that sustain it. Will it work? Moods and thoughts persist in old age. After all, eighty odd years of flowing thoughts lie in my memory!