Hello,
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Blood test and EKG being normal is a good sign.It seems you are suffering from anxiety which is the most common cause in young adults for racing heart.Relax yourself you are not going to die and avoid any stress.
1)Do some form of mediatation/yoga daily.It will help in combating the symptoms.
2)Reduce stress levels and do not be alone as you will keep on thinking.
3)Have healthy nutritious diet.
4)Go for a walk or jogging in morning.
Consider visiting a Physician as prescription medications as Propanolol are usually given for these symptoms.But personally I would advise you not to have medications at this age.
Take Care!