Suicidal thoughts can come into your head for no reason and this can be really frightening. It can be due to certain chemicals in your brain not working properly causing you to feel depressed.
Something physical that is happening to you can also cause suicidal thoughts, taking drugs, drinking alcohol, having a head injury in the past and even an under active thyroid which can be diagnosed with a simple blood test.
Some people attempt suicide but fail and can be left quite damaged, if you succeed it is final there is no turning back and the effect on the person who finds you and those family members left behind can be overwhelming.
Have a look at this link and read through the information given on the page, this may help you to seek help at a time you most need it.
There is also a new App "Suicide? Help!" see link below on google play