Generally, the symptoms of overdosing can range from deeply uncomfortable and distressing to painful. Many of the symptoms of overdosing, like intense headaches and vomiting, can be painful. Moreover, if you overdose and have to have your stomach pumped, that process is painful for some people.
If you are considering overdosing as a means for suicide, you should immediately call the National Suicide Prevention Lifeline at 800-273-8255. Your life has value and is worth protecting, and there are people who care who are ready to speak with you and offer help.