Is it normal for my dad to talk to himself?

over the past few months me and my mom have been seeing many changes in my dad. My dad is around 44 and we have noticed that he is started to talk to him self. Its not just a talking its a conversation with emotions and everything, its like hes actually talking to someone.Ives seen changes in his irritability level. He gets angry a lot more, he seems to be a lot more nosy on what is going, and to be perfectly frank he asks the most dumbest questions laity. The one day i sprayed bathroom spray and this is like the middle of winter, and my moms like OH lilacs and my dad is like ohh are they out, are they in bloom, and he kept asking these questions. I'm over extricating he asks these kinda things all the time. Please someone i need your help, whats going on with my dad? Im really concerned...