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Researchers now believe that tension headache may result from changes among certain brain chemicals — serotonin , endorphins and numerous other chemicals — that help nerves communicate . Common medications such as aspirin , acetaminophen ( Tylenol , others ) and ibuprofen ( Advil , Motrin , others ) may contribute to rebound headaches — especially if you exceed the recommended daily dosages . By studying the permutations that result from different patterns of mirrors acting on strands , Schlatter came up with rules deciding when a generalized lion 's stomach design , which always has an odd number of columns , could be drawn with just a single curve . This limited goal was met by the well-known union catalog model , where the library is represented as a set of uniform ( Dublin Core ) metadata records that reference resources via their URLs . With perseverance , most people break the rebound headache cycle within two months . Indeed , some sequences of notes result from little more than a slowly changing phase relationship between oscillations governing air pressure and those controlling labial stiffness .