I have b12 injections every 3 months. I just have noticed that roughly between a month to 1 week before my injection my resting heart rate increases from an average of 68 to 73. This has been the case for the last 9 months (since I've had a fitbit that measures hr).
To note, I have no fear of injections or worry about visiting the doctors.
Has anyone else noticed this or know a reason this may happen? I'm quite curious.