Why is my neutered male cat going crazy to get outside?

My four year old Himalayan accidentally got outside last week. He was out there for about an hour while I searched for him. Ever since I got him back inside, his entire life has been about trying to get back out. He hollars and cries all day long and has become incredible aggresive with me and my other cat. He is fixed, but could it still be the season? I'm absolutely heartbroken about his instant personality change. Can anyone tell me why this is happening and what I can do?