Is it normal that i got aroused seeing my parents having sex?

Okay, so my dad is renovating my parents ensuite bathroom at the moment and for the past week they have been sleeping downstairs on the pull out sofa bed in the living room. My mum is fifteen years younger than my dad and let's just say they have a very healthy marriage together. In fact, I have heard my dad tell his friends from work that my mum is a nymphomaniac and he often jokes that she will be the death of him one day. Well as horny as my mum is, you would never know it because she is actually rather shy about sex and easily gets embarrassed just having it come up in conversation. I guess you would say she is your typical librarian type who becomes a completely different person behind closed doors! Anyway, suffice it to say, I certainly wasn't expecting her and my dad to be getting up to anything outside of their bedroom. So when I woke up feeling thirsty last night, I just assumed the coast would be clear for me to go downstairs and get a drink as per usual. Thinking they would be asleep (it was well after midnight), I tiptoed down the stairs and made my way into the kitchen. My parents have one of those water coolers right next to the fridge, so I didn't even have to open the fridge door or make a noise turning the tap on. So far so good. Then I hear a click and the TV turns on. WTF? My mum starts giggling and my dad has to tell her to be quite, then I hear them start kissing and my mum is practically begging my dad for you know what! OMG, is this really happening??? Like seriously, right now, while I'm trapped in the freaking kitchen??? No sooner had that thought crossed my mind when I heard my mum let out a loud gasp followed by "oh fuck, my pussy!" and I just froze right there on the spot! Not knowing what else to do, I decided to wait until they were really into it and then I planned to just keep my head down and make a dash for it as quickly and as quietly as I could back up to my room. My heart was racing and I was so nervous that I began sweating and shaking. But what really disturbed me was the more that I stood there listening to the sounds, the more I actually felt myself getting physically aroused by my mum's moans and whimpers of pleasure! Yes, I know that's crazy, and no, I have never had any sexual feelings for my mum before ever. I am just your typical horny teenager. I don't even have any weird fetishes or anything. In the end I decided I had to get out of there! Upon turning the corner, however, I just couldn't help myself. Curiosity got the better of me and I sneaked a peek into the living room and OMFG! My mum was on top of my dad, all hot and sweaty, with her eyes closed and her head back, bucking and writhing on the end of my dad's cock going in and out of her shaved pussy as her DD breasts were going everywhere and it was all just too much for me! As embarrassing as it is for me to admit this, I don't think I have ever been so hard in my entire life! Like I'm talking painfully hard here! My dad then flips my mum onto her back and starts pounding her so hard and fast between the legs that my mum is squealing and she wraps her arms and legs around my dad, curls her little toes and digs her fingers into his back, all the while begging my dad for more! Oh man, just seeing the way her silky smooth, creamy white skin glistened in the light of the TV and the way she squealed loudly and curled her little toes for every thrust of my dad's big cock deep inside her wet pussy! I just couldn't take anymore and started jerking off right there while I watched them and busted the biggest load I have ever blown in my life! I had to take off my shirt to wipe it up off the floor and it was everywhere! Like my cock had just exploded like a cannon! I then went back to my room and had to jerk off twice more before I could finally get to sleep! I can't even remember the last time I was that freaking horny! And all of this was over accidentally catching my parents having sex!!! So is this normal that I got so aroused seeing my own parents having sex??? Oh and a part of me is actually wishing I could catch them going at it like rabbits again! I know, I know, but I can't help it! I swear it was the hottest thing I have ever seen! So yeah, is it normal to be having this reaction? Please, I need some honest opinions here!