I have it, fairly mild, sporadic with short-ish duration. Typical, when I was sitting at my desk, my normal resting heart rate of ~60 BPM would be going at 120, which is very obvious. Not hugely distressing, but it doesn't feel great.
At worst, it happens a couple times per a week for 1-5 minutes at a time. It seems to be worse in the winter when air quality around here is bad and it's cold, and dry and more often when I exert myself. It has caused me to quit training hard for xc ski marathons because if I get even a 5-10 minute bout of SVT during hard exertion like a ski race, it ruins the rest of the race, making me feel like I'm at max effort when I'm trying to go at an easy pace, and then has the same effect as if I did over do it - I more or less bonk and it takes a while to recover. I'm not super competitive or successful as a "racer" but they were fun and now they aren't. When it happens when I'm exercising, a heart rate that should be, say, a fairly easy 130 would jump to what I would consider nearly max, like 170+. From experience doing 50k races, I know that at that point in time, if I exceeded 155 or so for any length of time, it messed me up, my race pace was ~140 -150. So hitting 170+ was really a crash and burn scenario, and not fun. It pretty much made me stop and just shuffle for quite a long time to recover.
Things I've done to reduce it are (1) no more caffeine and (2) try to hydrate better. I seemed to notice that when I ski trained at noon after a couple of cups of coffee in the morning it was worse. I also tended to start the day pretty dehydrated after exhaling moisture all night in low humidity conditions. So I quit caffeine a couple of years ago and make a point of drinking a full liter or more of water before 10 am every day. It seemed to help, but it also corresponded to me reducing hard xc ski training so I can't really say. I don't miss the caffeine though, and nowadays, a caffeinated gel really gets me going for the last part of a long ride!
In the summer, I experience it hardly at all, and almost never (that I can tell) when riding the bike, even with events or group rides where I really push it. I'm not sure why - like I said, it could be the temperature, dryness and air quality in the winter that makes it worse. It could be that the quadra-ped nature of XC skiing taxes the cardiopulmonary system more than the bi-ped nature of bicycling? But I would think fitness would address that, and at the time this started bothering me (about 7-8 years ago), I was decently fit. I did three 50k's that year and had trained diligently to do so, and was well experienced in this sort of stuff.
I do know that sometimes when just feel like I'm not getting on it during workouts, riding or hiking in the summer, I can almost always trace it to having some SVT going on. But it just doesn't happen that often.
I have a friend who just went through ablation procedure because his SVT was so bad. He tries everything to convert, even plunging his face into ice water. I've never had it that bad. I think that sometimes "bearing down/ holding breath/coughing" sort of stuff might end my SVTs but it's not reliable.