Interpretation of Dreams. Freud, (4)

One, perhaps minor, source of dreams can be "imaginative visual phenomena," as Johannes Müller (1862) puts. This is applied to rapidly changing images floating before eyes in lethergic states like "hypnagogic hallucinations." For instance when you are hungry but are tired too and are about to fall asleep, you may have a vision, right before sleep, that a plate of food (your favourite dish) is in front of you or you are eating from it. This source can be either auditory or visual mostly. It has certainly happened to all of us that in those specific moments we appear to have heard a word, a hum, a song, or even our recently dead relative talking to us. Dreams occuring soon afte entering dark places may also be due to retinal exitations and are different from dreams occuring in the morning before waking have an objective stimulus like the light penetrating from the window to our eyes.
Still one major component dream stimuli is internal organic somatic stimuli. Strümpel (1877) remarks that "during sleep the mind attains a far deeper and wider sensory consciousness of somatic events than during the waking state." This justifies why Aristotle believed that the beginning of an illness might make it felt in dreams owing to the magnifying effect produced upon impressions by dreams. Thus dreams can be promonitors of illness, too. When the brain in no more involved in daily conscious activities, it can scan the organs during sleep checking their function. When people dream of being choked or having a terrifying end it might be due to lung or heart diseases of which the sleeper is unaware. Of course, not always such dreams mean hidden diseases. Healthy people, too, can have such dreams but with a different origine. A good example is when you dream you are searching for a WC in a hurry and upon waking you see that you really have a full scrotum. Why we have a better consciousness of night time pain is also due to scanning activity of mental life during sleep. Schopenhauer holds that our intellect takes the impressions of the world and remodels them into the forms of time, space and causality. At night when our intellect is no more deafened by the impressions of the day, impressions arising from within are able to attract attention to which (stimuli) our intellect reacts and dreams start.
If an organ is excited during sleep it can produce an emotion which triggers images in dream appropriately connected to that excitation eg if you have tooth ache you probably find yourself at a dentist's, or when you dream of falling from a height it can be due to the movement in sleep which makes your hand fall from the edge of the bed_tactile sense is unconscious, when there is a movement it should be activated. The transition from unconscious to conscious stage prompts images and illusions forming content of a dream.
The most important, perhaps, source of dreams is psychical stimulations. It happens that you dream of an unimportant event of your daily activity because it has been ignored by your intellect classified as petty and insignificant. On the contrary you may also dream of an important issue which has engaged your mind during daily life. The material of this sort come from memory either from afar (childhood) or close by and are all due to associations and reproductions of memory.