What has been going on in your life that is stressful? I would begin a journal. Write down what has been happening in the last few months. Include good things and bad. Things that are bothering you. Maybe some past issues that you've been thinking about or are affecting you today. You need to discover what is causing these attacks.
Personally, I wouldn't go out and get medication right away unless it was something like an anti-anxiety drug such as Ativan or Xanax. Those drugs you can take just as needed. I take Ativan every once in awhile, I don't feel weird on it. It doesn't make me sleepy. I just have less anxiety.
You may not need a long term anti-depressant. I'm not a doctor, I'm just going by my experiences and the knowledge I have gained about panic/anxiety attacks. Once you find the reason behind your anxiety, you may be fine. So, a long term med doesn't make sense (at least not now).
If you need help determining what's causing your anxiety, I would make an appointment with a psychologist. Cut out caffeine and junk food. At bedtime, don't sit and wait for the attacks. Distract yourself with a good book or your journal. When the attacks do come, use positive self talk and relax. Calmly relax. You can e-mail me if you need any more help!
At my worst, I had panic attacks several times a day, especially in the evening. The evening is the worst for me - if I am not actively practicing relaxation, going to therapy and on medication, I will have a panic attack every single night for sure! So you are not alone in having attacks that often, nor are you alone in having them in the evenings or at night - my panic is always at its peak then too. And, like you, I don't have "triggers" many times - the attacks pop up totally out of the blue.
No, the cannot kill you. I had my first panic attack at age 10 - have had them constantly for 22 years - and I am still here despite thinking that I have a terrible heart condition (my heart is as "good as gold" according to the cardiologist). Other than putting stress on your body and being exhausting, a panic attack will not cause a heart attack.
Start with therapy right away. A doctor might suggest medication, but I personally believe that therapy should be given a shot first before jumping into medication (although I am very supportive of medication if you need it!).