why did my heart rate become lower?

[ladidadi]

Hi,

First of all, hello everybody, I've just registered here. Oh and sorry for my english in advance, it's not my native tongue.
So here is my short history:
I'm a (soon) 31 years old guy.Since ca. 2008, i have heart anxiety (you know, measuring heart rate, reading about heart on the internet, PANIC ATTACKS every now and then, ...). Last year, I started to work on my bachelor thesis, so i was very nervous (obviously). I finished in October (around the deadline, i was experiencing chest pressure too), but the anxiety didn't disappear. Actually, it became worse. I started to focus more on my heart. Blood pressure, heart rate, ... AND panic attacks became more common too (with heart rate peaks at 150-170). I don't do any sport (just VERY little yoga since this january), I don't move much, but I'm very thin (lost around 7kg during 2016, in december i was 62kg). So i decided to change my diet. I went vegan (also gluten free), but it didn't help. I started to eat more and healthier, but that just made my digestion faster and the 2000-2200 calories i ate weren't enough (I THINK) so i lost even more weight (now i'm at 59-60kg).
constant anxiety, panic attacks 1-2 times a week.
resting heart rate WAS around 70-80
blood pressure ca. 100/60
when standing, my heart rate increases by 10-20 points.
walking slowly with my dog: WAS 110-120
my resting heart rate late in the bed (or after ca. 10pm) WAS 55-60 (same in the morning when i wake up)

i know, these values are actually pretty good, BUT here comes the question:
around 3 weeks ago, suddenly (within just a few days) my heart rate became a lot lower. during the day, i measure 55-65 at rest (as i said, it was 70-80 before, only in the evening i had this low). even standing i have like 68-75. even better(?): i was just walking with my dog and i had 74-84 HR...
i DO NOT feel myself weaker (i was already weak before). my BP didn't change (maybe just 2-4 points less both SBP and DBP). and my "evening" heart rate went down to 50-55.
i DO FEEL myself more calm, even though my head is still full with the same anxious thoughts (i know this sounds strange). my brain is somehow... less stimulated. but i'm still nervous... nervous-calm?  i cannot tell if the calmness made my HR lower, or my lower HR made me calmer (or should i say SLOW?).

why is this sudden change in heart rate? can it be a heart failure or something?

what i changed in my life around the same time of this change:

- my calorie intake is still the same, but i do eat meat and egg again (no dairy). but this can't be the cause, because I ate meat in my whole life.
- because I don't eat dairy, i started to take 1 calcium pill daily (just 250mg calcium-citrate). and i eat more sesame seeds (also because of calcium). my magnesium intake was always good, probably way too good (800-900mg/day).
- i changed my sleeping pattern. i still sleep around 7-8 hours, but i go sleep around 10-11 pm (previously it was 2 am)
- i started to read about christianity and jesus (don't laugh! who knows? :D i was scared)
- i eat only 5 gramms of salt a day. but previously i didn't eat any salt before noon. now i eat half of my intake before noon (i start my day with a glass of water with 0.5 gramm salt). oh and i drink 8+ glasses of pure water. ALWAYS did.
- and this is a BIG one: 1 pill of plant based high quality omega3 (just 450mg). i found a study, in which, college students took 1000mg omega3 daily, and after 2 weeks, their HR became 5.9 points less on average. could this be?

thank you in advance!

[ladidadi]

one more piece of information to add:
i experience some dull pain around the end of my sternum (or under it, NOT behind it) and also upper-middle back pain. but these just come and go. not related to movement (heck, i don't exercise, because i freak out if my HR is high). my sitting posture is very bad, i slouch a lot.