A method of rebreathing for a human, comprising: breathing through a rebreathing device for up to 20 minutes at a time, repeated as needed; wherein said rebreathing device has a form of a) cylindrical form made by rolling a sheet of paper, and able to fit snugly over either the mouth or the nose of a human in need of rebreathing; b) cylindrical form made with a cardboard tube from a toilet paper roll; c) cylindrical form made with a cardboard tube from a paper towel roll; d) cylindrical form made from a washable, re-useable, solid tube and able to fit snugly over either the mouth or the nose; e) rectilinear form made from a paper bag made of absorbent paper, at least 5 inches long [=12.7 cm] for adults, that is modified by i) cutting or tearing horizontally to shorten the bag so the remaining bag is approximately 5 to 7 inches [12.7 to 17.8, cm] tall, and ii) folding over one corner of the rectangular bottom approximately 1 inch [=2.5 cm] and cutting or tearing it off to make a hole approximately 1.5 inch [=3.8 cm] in diameter to allow rebreathing when worn over the nose and mouth; f) triangular form folded in the shape of a mask able to cover both nose and mouth made from i) a sheet of paper size 8.5×11 inches [=21.6×28 cm], A-10, or any larger sheet of newspaper folded down to this size, or made by folding a foil-lined snack-food bag of approximately 6×10 inches [=15.2×25.4 cm]; or g) conical form made from a paper, foam or plastic disposable cup, into which a hole is made in the bottom about 1 inch [=2.5 cm], which need not need to be centered, so that the original cup opening may be placed over the nose and mouth and pushed lightly against the face so that it forms a snug seal all around.