Hey you with the chronic hypermobility and/or orthostatic intolerance issues
If you have a menstrual cycle, has anyone told you how it affects your chronic illnesses?
Probably not so I'm gonna!
First here's a basic chart showing the large fluctuation in hormones during your cycle:
If you have hypermobile joints, the level of estrogen in your body will heavily impact the stretchiness of your connective tissue. During ovulation, estrogen has a huge spike, which will make you extra stretchy! You are more prone to injuries, subluxations, dislocations, and general joint issues during this time. There's also a smaller increase in the week before your period, which can also affect joint laxity.
If you have orthostatic issues (or even if you don't, tbh), you'll be interested to hear that both estrogen and progesterone affect your heart rate. Generally your resting heart rate will be higher in the days before your period due to rising progesterone levels, and then drop back to normal after your period starts and progesterone levels fall. Estrogen is also at its lowest level during your period, and with low estrogen levels comes a higher number of heart palpitations and potentially a higher heart rate, depending on the person.
This combo of low estrogen and high (and then low) progesterone, plus the whole bleeding thing, means you're extra susceptible to dizzy spells, presyncope, and fainting in the few days right before your period and the first couple days of your period (and if you have a heavy flow, this can continue longer). It also means you might feel a lot more stable, less dizzy, have less heart palpitations etc around ovulation due to the extra estrogen.
There are a bunch of other bodily functions, chronic illnesses, etc that are affected by hormone levels during our cycles, and there are some good resources online about what these hormones do — I didn't even talk about FSH or LH, the two other big hormones that are part of our cycle! But I didn't want to get too far into the weeds in this post.
PS there's a theory that the reason more AFAB people (even many without a uterus or menstrual cycle, AFAB hormones are Kind Of A Bitch) get diagnosed with things like chronic fatigue syndrome, hypermobile disorders w/chronic pain, POTS etc is because we have a built-in flare up every month (sometimes two, if you flare up at both your period and ovulation). So it's just much more noticeable in AFAB people because AMAB folks don't have to deal with those built-in flare ups every 2-3 weeks.