Suggest Remedy For Persistent Vertigo
Some initial blood tests are necessary.
Detailed Answer:
I read your question carefully and I understand your concern.
Judging from that description I think one common cause to be searched for would be anemia. Anemia can cause a clinical picture of fatigue and light-headedness, at times when the brain doesn't get enough oxygen (due to the low concentration of blood cells) may lead to syncope (fainting).
Other possible causes might include a metabolic (blood glucose, kidney function, electrolyte) or hormonal imbalance (thyroid or glucocorticoid function). A heart rhythm abnormality is another less likely cause.
So I think some necessary blood tests are necessary, routine ones, such as blood count, blood glucose, liver and kidney function, electrolyte, thyroid function. Afterwards further steps depend on the results, if they indicate any abnormality more exams for the cause might be necessary.
I remain at your disposal for other questions.
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Detailed Answer:
Hello again! I am sorry that your daughter is still not feeling well. However the fact that the tests are normal and the doctor has noticed nothing apart from low blood pressure is good news and you should feel reassured and reassure your daughter as well. Remember that she is at an age where the body undergoes many hormonal changes and such manifestations can be transitory benign occurrences.
While I do not know her values, low blood pressure does explain those signs which you mentioned. So the recommendation for increasing intake of water and salt is a valid one.
However if symptoms are a regular occurrence it should be looked more in depth. You do not mention whether any hormonal level was done, if symptoms persists thyroid function tests which I mentioned are necessary as well as some other hormones such as cortisol (perhaps already done, saying in case they haven't been included).
Also a condition called Postural orthostatic tachycardia syndrome should be considered. It can manifest in teenagers with a predomination in females. It is due to hormonal and growth spurt alterations, but decreases over time. Its characteristic is a change in heart rate when changing position which can lead to all of your daughters symptoms. Perhaps your doctor already considered that and performed heart rate and blood pressure measurements supine and standing, but not all physicians are aware of that condition so it should be discussed with him.
If all the above have been done then a more prolonged study of heart rhythm might be necessary. A simple EKG studies heart rhythm at that moment in time, but there are transitory arrhythmias which can be detected by using a Holter portable rhythm monitor which monitors heart activity over 24 hours while the patient performs usual daily activities. If headache persists or increases in intensity a head MRI might be necessary as well.
Of course I am not suggesting all these tests are done right away in a rush. For now urgent life threatening conditions have been considered by the doctors, these are more step by step measures in case symptoms persist or progress over time despite the water and salt recommendations and a healthy lifestyle. As I said most commonly are transitory changes and above tests may not be needed at all.
I hope to have been of help.