Medications cause heart palpitations too. When I was young, I had hypothyroidism and had to use synthetic hormones. Those gave me tachycardia in the beginning. I was not alarmed though because my doctor had already warned me of this side effect.
I also experienced bradycardia once due to a blood pressure medication that reduced my heart rate too much.
If anyone is on new medications and has started experiencing heart palpitations, the medications may be the cause. It should be listed in the side effect although sometimes it does occur that the drug company doesn't list it.