Is it normal for an elderly person to not want to wear a jacket going outside in 30 degree weather? What may be the reason behind that?

My father-in-law lives with me and my husband and has been since my mother-in-law passed away. He is 81. We are very confused about his outlook on life. He doesn't eat healthy unless he is scared something is wrong. He is able to drive, balance his check book, live a normal life. But there are times we are not sure if he is normally functioning or not. He has diabetes, hypertension, arthritis, and is on medications. He only visits his doctor once a year, but never follows directions. We obviously can't force him to do anything, but we get worried when he acts strangely every so often. Lately, he has been sleeping a lot more than normal and going outside in the cold without a jacket in 30 degree temperatures.