Having heart palpitations in the evening after using coconut oil when hypothyroidism is present may be explained as having the thyroid finally kick in and induce those rapid heartbeats. Those with thyroid problems report on curezone that use of coconut oil cleans this condition up. Try "Oil Swishing" forum as regards orally swirling coconut oil in the mouth for 20 minutes and spitting it out. This sucks lots of infection out of the sinuses and gums; cleans and whitens teeth by cutting biofilm; and can start clearing up what may be a sub-acute fungal infection of the thyroid suspected because coconut oil has a powerful anti-fungal, caprylic acid. Blessings!
Adrenal Fatigue Connection
Don't forget adrenal fatigue. I had heart palpitations and tacchycardic states for several months before finally being diagnosed with adrenal fatigue by a homeopathic doc (western medicine docs don't recognize this condition). There are tons of natural remedies, just google adrenal fatigue.