Double heart beat? or just anxiety?

after taking a shower last night,
i got a class of water then just crashed out on my bed.

i noticed that my heart rate slowed down alot.
i dont know if it was because i went from standing to laying so fast
but when i noticed my heart beat it went

thub-dub....thub-dub...thub-dub-dub...…

and it freaked me out becuase ive never had a heartbeat like that
so i kept feeling to see if it continued but it never did. and ive been monitoring my heartbeat all day today and i didnt hear it once again...

like i said, i dont know if its because the change in standing to sitting so fast
ive had EKGs done xrays blood test you name it. everything normal.

my heart rate does change when i breathe in and out but thats normal (sinus arrhythmia)

i've never had heart problems in my life. im 19 and exercise regularly. do not smoke

ive been paranoid about it all day can anyone please help me out?

id appreciate it

[is_something_wrong]

One word. PACs. Completely benign. We all have them. Nothing to worry about! :)