Morning boners

Lola ๐Ÿ’๐Ÿป๐Ÿ’• โ€ข 21 ๐ŸŽ‰ Not ttc, been with my partner for over 2 and a half years and adore him ๐Ÿ’• mummy to 2 furbabies๐Ÿฑ๐Ÿถโค๏ธ
When a guy has a boner in the morning when he's asleep, does that mean he's having a sexy dream, or is it just a biological thing that happens on a reg basis?