Hello, Diet pills should always be taken in low doses & short term use is the best. You should exercise regularly, do walking, stretching, avoid trans fat, oily, spicy junk food, refined flour, salty and sugary food items. Take more of whole cereals, vegetable protein, fruits and veggies. Take small meals & adequate sleep. Some diet pills cause heart palpitations & rapid breathing as they contain caffeine, guarana or amphetamine based ingredients. Diet pills reduce your appetite and increase your metabolism & this may trigger tachycardia if you have history of some heart ailment. Low blood pressure may be caused by dehydration, Stay well hydrated. Avoid heavy work & take rest between work. Diet pills reduce fat absorption in the body thus interfering with normal metabolism & causing symptoms like dehydration, bloating, nausea, anxiety, etc. You are suggested to report your symptoms to your treating doctor so that the doses you are taking can be monitored(tapered) or medicine replaced by some other pills that suits you better. Get a heart check up done to stay on the safer side. Get lipid function tests, EKG, stress tests done. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Nupur K, General & Family Physician