The Mandukya Upanishad is a philosophical text found in the Vedas, which are among the most important scriptures of Hinduism. Here is what V. Subrahmanya Iyer says in a foreword to a translation of the Mandukya Upanishad:
While [the Mandukya Upanishad] shows how the most advanced modern sciences and modern philosophies are approaching its conclusions, it gives to the world of our own times its central doctrine that partial data give partial truth, whereas the totality of data alone gives perfect truth. The ‘Totality’ of data we have only when the three states of waking, dream and deep-sleep are co-ordinated for investigation. Endless will be the systems of philosophy, if based on the waking state only. Above all inasmuch as this philosophy holds that mere ‘satisfaction’ is no criterion of truth, the best preparation for a study of Vedānta Philosophy is.a training in scientific method, but with a determination to get at he very end: ‘To stop not till the goal (of Truth) is reached.’
Personally, as a Hindu myself I am skeptical of V. Subrahmanya Iyer's characterization of the Mandukya Upanishad, but I am still interested in his quote for its own sake.
Empirical science focuses on what the mind experiences in the waking state, i.e. information about reality that is gleamed through the senses and, I suppose, through introspection of one's own mind. But my question is, have there been any thinkers who have formed a theory of reality which takes into account not just data from the waking state but also what the mind experiences in the dreaming state and the state of deep sleep?
I should mention that the reason V. Subrahmanya Iyer characterizes the Mandukya Upanishad in this way is that he interprets it as making the argument that just as in the waking state we find that all the objects in our dream are not there anymore, within a dream we find that objects of the waking world are not there anymore, so both objects in the waking world and objects in dreams are equally unreal. But are there other thinkers who have used our experiences in dreams to form other conclusions about reality?