The Mayo Clinic reports that a normal heart beats 60 to 100 times per minute. Tachycardia occurs when the heart beats too fast and this beating can be raised significantly above the normal level. This can be very uncomfortable for the sufferer and in some situations tachycardia can be life-threatening. Low blood volume leads to tachycardia because the heart is trying to overcompensate for the lack of blood volume in the body. It causes the heart to overwork, beating quicker and quicker to try to keep enough blood going to extremities (such as feet, legs, arms and hands) and to the brain.
A low sodium level in the blood may result from excess water or fluid in the body, diluting the normal amount of sodium so that the concentration appears low. This type of hyponatremia can be the result of chronic conditions such as kidney failure (when excess fluid cannot be efficiently excreted) and congestive heart failure , in which excess fluid accumulates in the body. SIADH (syndrome of inappropriate anti-diuretic hormone) is a disease whereby the body produces too much anti-diuretic hormone (ADH), resulting in retention of water in the body. Consuming excess water, for example during strenuous exercise , without adequate replacement of sodium, can also result in hyponatremia.
A sign has the potential to be objectively observed by someone other than the patient, whereas a symptom does not. There is a correlation between this difference and the difference between the medical history and the physical examination . Symptoms belong only to the history, whereas signs can often belong to both. Clinical signs such as rash and muscle tremors are objectively observable both by the patient and by anyone else. Some signs belong only to the physical examination, because it takes medical expertise to uncover them. (For example, laboratory signs such as hypocalcaemia or neutropenia require blood tests to find.) A sign observed by the patient last week but now gone (such as a resolved rash) was a sign, but it belongs to the medical history, not the physical examination, because the physician cannot independently verify it today.