Electro-Convulsive Therapy

After a recent suicide attempt, I was diagnosed with major depression. I also have dissociative episodes that last from a couple of hours to a week or more. My antidepressants are causing severe side effects (irregular heartbeat, migraines, nosebleeds, vomiting), which are increasing in frequency and severity. I was told to consider ECT. How effective is this treatment? What are the risks?