I should probably clarify, heart rate and heart rate variability are different. So yes, heart rate will climb just as we're about to have a meltdown, but it's possible that HRV will drop before then, giving us advance warning. I'm not sure though, I'm only just starting to look into it.
One thing that's puzzling me is how to judge whether ones HRV is normal or too low, as there don't seem to be many charts around, and some of them measure it in different ways. Like sometimes they just use a 5 minute measurement, which will give different results to the overnight measurement I get from the Fitbit. And I've read that the measurement on the wrist is less accurate than, say, chest monitors. At first I thought my reading was too low but now I'm not so sure and I don't know how much I can rely on it.
All I know so far is that yesterday, for example, my HRV dropped to 25 ms, and that corresponded to me feeling a bit under the weather. Today it's risen back up to 28 and feeling a little better.
Anyone else got any measurements they could share?