Need help understanding HRV

I'm a bit confused by your post.  You end by stating that you are having some medical issues then note that your HRV has been low off and on for a while. Although I can certainly not say that these are related, it would not be unreasonable to suspect the unbalanced HRV is an indicator for the medical issue.  Keeping in mind that the HRV is derived from a watch and algorithms, I would always be careful reading too much into it but I do see a rough correlation between an unbalanced HRV and illness in my case.

As low (in comparison to each individual normal values) HRV can be an indicator of some form of stress (such as illness), I'm not sure what you are asking?  I'm not sure the Garmin watch forum is the best place to be asking "should I be worried" when dealing with a known (or under investigation) medical issue. I'd say focus on the medical issue (you can mention the HRV factor to your doctor although I doubt it will be considered important).

It is only my iron level that is being looked into, nothing else. It's just the blood test also showed something else but nothing has been explained by doctor as they have just asked for another blood test. 

I don't understand HRV hence why I was asking

You are likely better to search more information on HRV but always remember that there are limitations on obtaining it from a optical heart rate sensor on a watch and then the algorithm to interpret it for each individual person.  A very short description (and I’m sure people will step in to add details) is HRV is the measurement of the small ongoing changes in the heart rate. The interesting this is that when everything is good then HRV will be higher. Under stress, which is a general term for illness, stressful situations etc, the body produces hormones that will make the HR more regular, hence HRV goes down (not up).  With your watch, over a period of time a baseline is established then anything outside this is reported as unbalanced. It must be taken with a grain of salt but for some people it correlates well with illness, injury or stress.  obviously I have no idea in your case if things are related but I would still just focus on the medical side of things. 

Both HRV (and VO2max too) have natural seasonal variability. So it's perfectly possible that your HRV really has been going down towards the winter. And since it's a real physiological thing, there's nothing to do, except to wait for the HRV baseline to eventually catch up, or the spring to arrive. How large the seasonal change is depends a lot on the individuals and where they live. Up here in Finland I've gotten used to the fact that my VO2max drops 2-3 points for the winter (this has happened on 3 different watches from different companies), and now I clearly see it with my HRV as well (now that I have Forerunner 965 that measures it).

No, you shouldn't worry but not ignore it as well.

HRV values may get worse according to high stress levels, high cortisol levels, overtraining, insufficient resting, bad sleep, psychological or emotional condition and some kind of ilness such as flu. It may be a sign of cardiological problem but rarely.

How about your vitamin D levels ? Vitamin D deficiency is the key reason of the most problems, it weakens the immune system. It can even cause auto-immune diseases such as Hashimoto's.

How about your daily average stress scores ? Has it increased ?  How about your resting heart rate ? You most likely doesn't rest enough or your stress is higher than normal.

Check my story here, how flu affected my stress and HRV values;

forums.garmin.com/.../can-fenix-7-pro-detect-illness-let-s-have-a-look

Hrv is busted in 15.77. No flu, 8 hours per night sleep, regular exercise. Great diet with supplements to cover everything. Still low hrv. The watch had me undo a lot of training and just recommends a rest day every day 

I am not a physician to interpret the health snapshots with great certainty, but the watch reports do really indicate something about  my physiological condition and how I feel, much more than I would have expected.  In my case the hrv really follows my sleeping, stress, exercise and energy levels....