okay, there's alot of debate on what IQ tests actually measure but what we know for sure is that it measures ur mental age. and u divide ur mental age by ur real age and multiply it by 100 and there's ur IQ.
its usually normal for it to drop slightly over a long period of time but what ur describing doesnt seem like that. im sure its something else. maybe ur just stressing or not understanding the question or what they want.
i dont know all the details but IQ tests can seem unnessary, like the answer to the question above is 1600 but u wouldnt know it unless u knew stuff about numerology. IQ tests just indirectly try to see what u know.
idk specifically why ur scoring lower on ur IQ tests but just take another one, but this time just relax and clear ur mind and focus on each question. just take it like the first time u took it. just focus on the tests. if u still make a low score then maybe there is something wrong. go to a T and see whats up. im sure its nothing to worry about. good luck with that. wish i coulda been more helpful.
best of luck.
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also.. do some research on IQ tests, i did some a couple yrs back and there's some stuff about how creative ppl and book smart ppl score different. i didnt want to bring it up here but it's interesting and it may answer some question. wish i had a link for u. sorry. well, good luck.