How do I convince my boyfriend he needs to get help?

We have been in a relationship for 2 years now and over time he has had many severe mood swings in which he breaks something (doors, tv, bed frame, phone, etc.) and then has a period of about two days where he will stay angry and slam doors, not talk to me, sleep on the couch, etc. After those two days he comes to me and apologizes for all that he has done and makes it up and everything is just fine. But my emotional distraught is not what I'm asking about. Never once has he raised a hand to me and these episodes seem to stem from almost nothing and really freak me out. We are a very agreeable pair when he is fine and these periods usually happen about once or twice every six months. I am concerned about him and I think that seeing a psychiatrist/psychologist would be a good idea. How should I tell him he needs to do this without hurting him or making him angry that I mentioned it. Please do not give advice such as "You need help or I'm leaving." That's not what I'm looking for. We have been through thick and thin together and I want him to get help because I love him and if I am hurt when he has these periods then he must be hurting too, and much more than I. Any personal insight and/or experience would be very helpful. Thank you.