question: Hi doctor,  I am a 26 year old healthy male. My height is 178 cm and weight is 73 kg. I do exercise regularly and I am healthy too. I have recently visited a cardiologist and done a cycloergometric test (Bruce stage 4 protocol). During the test my blood pressure remained normal but my heart rate increased very high to a level of 194. Without the ability to regulate my pace I felt as if I hit the wall. I felt very lightheaded, slight blurry vision and tingling sensation in legs. When I run the same thing happens every time, so it is not a single occurrence. My resting blood pressure was 132/80 mmHg. Sinus rhythm in ECG was 113 per minute. During the test we exceeded the maximum load of 5% and 111% maximum heart rate for the candidate's age (194bpm). Blood pressure increased to 160/60 mmHg. Base ECG at maximum load does not change much. Blood pressure was normalized in two minutes.  When I stand up after sitting for a while, I get blurry, black out vision which is often severe. My breath is quite shallow. I feel tired most of the time and muscle fatigue. The symptoms always worsen when hot or dehydrated. I did the "standing up test" on my own. I measured my heart rate while I am sitting relaxed for several times which are 62,64,67,70 and 73. Zero to two minutes after standing up the values are 74,88,90,97 and 93. After two minutes it is 77 and after five minutes it is 84. There is an increase of around 30 bpm in the first two minutes. Quickly going from lying down to standing up heart rate jumps from 63-105. What causes this and how can I fix it? So far I tried to increase my water intake. I have tried drinking a lot still I feel dehydrated. I also tried increasing my salt intake.