First, you aren't going to die. SVT is very scary, but it isn't fatal. I have had it periodically since I was in my 20s, I am 60 now and I'm still here. Stress is one of the main triggers, so try to calm down if you can. Take deep breaths and try to relax your muscles when you are lying there at night. It will help relax you. Keep busy during the day with things that keep your mind on something other than how your heart is beating. I sometimes can stop an episode before it really gets going by holding my breath and bearing down real hard like I'm trying to go to the bathroom. That works well for a lot of people.Hang in there until you can get to the cardiologist. You will not die.
There are a couple of things you can try to convert them to normal rhythm.
1) Valsalva. Sit on a step so your knees are brought up towards your chest. Take a shallow breath and bear down. Tense you stomach muscles keeping the force up high rather than down towards your bowels. Hold it for no longer than a few seconds. It's the initial rise in pressure that causes the conversion, not the duration that you hold you breath. Relax. If you still feel it, repeat.
2) Head stands. Don't ask me why, but several people here report great success with head stands again a wall.
3) Ice water face plant. Use a large bowl filled with ice water. Insert just your face, not your entire head.
I had the AVRT type of SVT all of my life, from 6 to 60, 54 years. I learned after the first episode how to convert them, and never had to go to the ER; literally hundreds and hundreds of episodes. I had the self sustaining variety that would not spontaneously convert on their own, but would run on for hours if left to do so.
Many find that as they age, episodes become more frequent. Mine had become as many as 3 to 5 times per month. If you get several episodes a month, I'd look into an electrophysiology procedure. I had one 4 years ago, and it eliminated them for good.
I've been dealing with the same for many years now and all I have to say is I agree with the other posters. First, it will not kill you. Second, if it gets really bad and they become very frequent you can look into an ablation..
I have had 8 episodes of SVT/Afib/Aflutter since 2006. I was converted at the hospital on the first 6, with a Cardizem injection the first 2 times with immediate conversion, then a Cardizem drip the next 4 times taking about 12 hours each. The last 2 converted at home in about an hour with a 600mg dose of propafenone (pill in the pocket). I tries Valsalva and ice water to no avail, mine are sustained and do not convert without chemical intervention. I consider them to be an inconvenience and certainly not life threatening unless allowed to continue for days (weeks?,months?). An ablation may be in my future if they become too frequent.