Just saw your post now. Personaly, you could start by reading about it and take one of the quizzes here on psychcentral. But be aware that it can give you a false positive depending on your interpretation of the questions and how you see things that day. Then a psychiatrist will have a long interview with you to discuss your life from childhood to today. He will also test you with one or two questionnaires (one is for all mental illnesses and the other, a personality test). The first time I was there, this whole process took almost 3 hours. But be aware, everybody has ups and downs, and we all respond differently to stuff that happens in life. Some will be more affected than others but it does not necessarely mean that someone is bipolar. Almost everyone in this society is affected by seasonal changes. One thing for sure that should be checked first, is your thyroid gland. An imbalance or Hashimoto's can mimic bipolar and/or depression, mood changes and increased or decreased energy. This gland can sometimes be working too much or not enough and can also alternate in the process. I hope you and your friend are doing fine and that you found answers to your questions. Take care.