I was very lucky with my diagnosis - it took about 8 months from first experiencing what I now recognise as POTS symptoms to formal diagnosis. It was so quick for me I think because my symptoms came on quite acutely so I was hospitalised and had all the tests done as an inpatient which speeds things up. I am now under the a national Autonomic Unit for management. However, we've now realised that my POTS is secondary to hEDS and it has taken about 20 years to get that diagnosis!
In terms of self management, I do the usual recommended things: raise the head of my bed so I sleep at an angle, leg strengthening exercises, drinking a pint of water before trying to sit upright in the morning, increasing salt intake (only as recommmended by a doctor), increasing fluid intake, eating 'little but often', wearing medical compression tights, calf pumping upon getting up/standing, avoiding triggers of prolonged standing, heat, eating full meals and, for me, sugar and caffeine. I tried these lifestyle changes for about 18 months before I was put on medication, which I now take.
It has hugely affected my life, but this is in the context of my EDS and the other autonomic issues that regularly accompany POTS. It affects different people in different ways. I lost my job, my place on my masters, many friends, have had long periods of hospitalisation and being housebound, have been at times unable to be left alone or able to go out unaccompanied, have lost five stone, now use a wheelchair when outside of the house, been unable to travel; in short, it has completely changed my life. I experience my symptoms every single day to different extents: there have been times I have been very ill and others when I've felt close to being well again. Fatigue is a really annoying symptom, as your body is working three times as hard as a normal person's body, so it can be frustrating to feel so tired all the time. POTS also flares badly when you have a 'normal person' illness to deal with on top - a chest infection put me in hospital for 2 weeks! It's this unpredictability I find most difficult to deal with.
I would recommend that you perform the 'poor man's tilt test' or active stand test at home with your husband - at different times of the day and under different circumstances (first thing, after eating, fasted, in hot weather, evening, when feeling symptomatic etc.). Get your DH to lie down quietly for 10 minutes to get a good resting HR. Then get him to stand up and take his HR at 2, 5, 7 and 10 minutes. A POTS diagnosis requires a sustained rise in HR of 30BPM+ or a sustained HR rise to 120BPM+ (usually in the absence of any change in BP but unless you happen to have a monitor at home you won't be able to tell!). Take these readings to your GP/specialist when you go.
I really hope your husband gets some answers soon - happy to help further if you have any more questions. Keep pushing for answers and testing and make sure you get referred to appropriate doctors with an interest in POTS (there's a list on POTS UK website). There will undoubtedly be questions raised about your DH's mental health and stress/anxiety but stick to what you know in your guts to be right and don't allow yourselves to be fobbed off - many POTS patients are misdiagnosed with anxiety/panic disorder owing to the similarity of the physical manifestations of an episode.
All the best to you both. At the end of the day POTS can be life altering but is not life threatening and life can go on, albeit sometimes in a different way to which we imagine for ourselves 💐