Brief Answer:
Several possible causes

Detailed Answer:
I read your question carefully and I understand your concern.

Symptoms such as weakness and rapid heart beats are very common and could be a manifestation of many different causes, not of only a single one. So in order to identify the cause more info and tests are necessary, to pinpoint the responsible one.

One possible cause would be an infection. Most infections may cause weakness and tiredness. Fever can be associated with increased heart rate as well. So especially if you have increased body temperature it is a possible cause.

Another cause would be anemia. Because there is a lack of sufficient red blood cells which supply oxygen it can manifest with lack of strength and tiredness. As the heart tries to compensate by pumping more blood it increases heart rate and lead to heart beat sensation.

Hormonal issues or metabolkic abnormalities can be responsible as well, such as high thyroid function for example. Last but not least anxiety can be a very very common cause, it would explain all symptoms including the tingling in the legs..

So if these sensations have been persisting I would suggest some routine blood tests which could differentiate between the above listed causes. Such tests would be complete blood count, ESR and CRP, blood glucose, liver and kidney function tests, thyroid function, electrolytes. Further steps (if necessary) will be guided by the results.

I remain at your disposal for other questions

---