Why does one get a headache after being forcibly awakened from a dream?

Question: Why does one get a headache when forced to wake up from a dream mid-way, but no headache when waking naturally after the dream finishes?

Answer: Dreaming is done by the manas. When the manas has matters on its mind and is not tranquil, it will manifest them in dreams. If the dream is suddenly and forcibly interrupted, the manas's intentions remain unresolved, and it will feel distressed; when He feels distressed, He causes a headache. This is an example of the mind influencing the body. Whether the manas is pleased or displeased, it will engage in some kind of activity, which manifests in the body—for example, dancing with joy, beaming with smiles, trembling all over, hair bristling with rage, and so on. From these phenomena, it can be seen that the manas has feeling, and not merely neutral feeling (upekṣā-vedanā). When a dream is forcibly interrupted and one immediately wakes up, one also immediately feels a headache. This headache has nothing to do with the mind consciousness; the mind consciousness merely feels the headache. What prompts the headache is the manas—He had something He wanted to do but could not finish it, and being displeased and unable to bear it, He needs to vent it out. If in daily life you frequently recite mantras and practice recollection of the Buddha (buddhānusmṛti), keeping the mind pure and free of concerns, you will no longer dream, and your sleep quality will improve as well.