I'm sorry that you have cancer. It's a terrible disease that nearly took a parent from me (it had metastasized before it was caught; my mother was incredibly lucky). I don't intend to trivialize it by any means, but I do think it's important to compare it to something like bipolar disorder.

Malignant cancer will probably either be dealt with or kill you on a time scale of 5-10 years, and although mortality rates vary, your chances of surviving many forms of it, particularly if it's caught before it metastasizes, are decent. Yes, there's a chance that it has gone into remission and might come back, but that chance goes down every year it hasn't happened, to the point where you're generally considered 'out of the woods' if you've been cancer free for more than 5 years. It's in many ways an acute disease: you have it, and it either kills you or you get better. Treatment is acutely unpleasant, but unlikely to kill you and although it can leave you with health concerns (if I remember correctly, it can cause osteoporosis in some people), for the most part you are done with it after less than a few years of chemo+radiation therapy.

Compare that to being diagnosed with bipolar disorder at the age of 20. Life expectancy in the US is almost 80. You don't really get better from bipolar disorder: you can be stable for a long time, but you never get to the point where you're considered to be 'out of the woods' with regards to having more mood episodes. That gives 60 years of dealing with a disease that has a high mortality rate and incredibly unpleasant symptoms; mania sounds great until you realize that it can mean experiencing full blown psychosis: walls melting, seeing people where they aren't levels of crazy. About one in three (25% to 50%) of bipolar patients attempt suicide at least once; one in five will die from suicide. As has been pointed out elsewhere, that is a higher death rate than some cancers, and that is -one of- the ways it can kill you.

The treatments, too, although not as immediately unpleasant as chemotherapy, are honestly potentially worse and cause more chronic concerns. They can cause other chronic problems that can kill you (liver failure, weight gain, weight loss, diabetes, thyroid dysfunction, lithium toxicity/lithium, weight gain, diabetes, associated heart issues/depakote+antipsychotics, PCOS in women/depakote) or be debilitating (dystonia, tardive dyskinesia/antipsychotics). It should be a sign of the severity of some symptoms that it's considered an acceptable trade off to have muscle spasms or uncontrollable facial movements for the rest of your life, sometimes in ways that are debilitating enough that you won't be able to walk. Note that these aren't the disease, these are the side effects that're considered 'less bad' than experiencing the actual symptoms of bipolar disorder. Many of them are permanent and will continue even if the medication that caused them is stopped.

These are some of the -common- serious side effects, not all of the common side effects (there are lots of other common ones that effect quality of life, including hair loss, sexual dysfunction, memory failure, etc.). With regards to rarer side effects, lamictal can (rarely; 1 in 1000 or 1 in 10000) cause your skin to fall off, particularly if your dose is increased too quickly.

Schizophrenia is generally worse than bipolar disorder, and the treatments are often similar (less lithium, more antipsychotics).

Both are chronic conditions that, when they are bad, can keep you from working, finding housing or living a normal life for however much longer you live.

I wouldn't wish cancer or bipolar disorder or schizophrenia on anyone. But I'd probably wish for cancer over severe bipolar disorder or schizophrenia.