Why am I suicidal and depressed for a period of time, and then not at all, and then depressed again?

One possibility could be that you have a bipolar disorder but I wouldn’t assume anything till you talk to a doctor about it. If it’s really long periods of time it could be seasonal depression. That’s when you get depressed usually in the colder months of the year but when they’re over you’re ok again. It could also just be the amount of sunlight you’re getting. Trust me, the sun really helps. It could be many things depending on your situation so i would consult a doctor or therapist to help figure it out.

Its very common for people with depression to feel this way. Its often a trait of bi-polar depression. You might feel high one minute and then low the next.