Cat getting spooked

I think my cat is getting spooked. At night he sits in the back porched (with windows) and I go to look for him and he'll turn around and his tail is hugh and all puffy. Sometimes he'll run in the house and go to the back window and his tail is going crazy. Another time I called him and he hissed. He has never done that ever as long as we have had him. I could not belive he hissed he has always been so calm and nice. I wonder if I spooked him. He is about 2 1/2 yrs old and this is the 1st time he has ever looked like that. I have check out side to see if I can see anything and there is nothing? He is the best cat I have ever had. He doesn't even meow!

There are animals outside and that's what he's responding to, whether or not you can see them. You need to keep him from looking outside so routinely or he'll end up turning around one day and attacking you (displaced aggression). It's one thing to occasionally look out the window during the day, another to get fixated on who knows what all night. It's like he's taking a course in becoming feral :-)!

He is an indoor cat so I figure it's ok to look out the windows. So maybe I shouldn't at night? He is so skidish when it comes to other things. I work from home so he is always with me he follows me around. I'll keep an eye out to see if things change.