Ok, this is going to sound a little silly,
I believe you. I've had a similar experience, though not as severe, when I was in my mid teens. I suspect that only those that have experienced these types of things can relate, because these types of experiences cannot be explained, and you know it when it happens.
My friend was with me at the time. We were staying at his house and had gone for a motorbike ride. No one was in the house, as his mother and sister were on holidays. The house was isolated on an acreage.
Anyways, we had parked up just under the house (it was on pylons). It was late afternoon. We were getting ready to go inside when we heard a noise from inside. It was coming through the floorboards and was only a few metres away, over our heads.
It wasn' what we saw but what we heard - I can only describe it as a disembodied voice that penetrated through the house, speaking in a language we had never heard of. It sounded deep and evil.
My friend and I looked at each other to verify what we had heard. We got back on the bike and didn't return for a few days. There were no signs of entry in the house. We still talk about this incident. We both agree it was something paranormal and it wasn't good. It still gives me goosebumps.
We spoke to his mum about it later, and she told us she had seen something years before at the house that looked like a Chinese man dressed in mandarin style.
The same friend and I saw something else that still creeps us out. Again, we had been bike riding, in a forest, and were parked in a clearing to have a break and a ciggie. I saw something through the bush (Aussie low lying scrub with gum trees) probably 20-30 metres away, which I thought was a gigantic kangaroo - it was absolutely massive, with short brownish-grey fur - I guess 7 foot high. It was just standing there. I pointed it out to my friend and he freaked out. It turned its face to us, and it wasn't any kangaroo, or anything we had seen ever. It was vaguely humanoid, and that's all I can remember now.
It just stood there, looking at us, unmoving. I freaked by that stage too - and guess what - my old Yamaha GT80 decided it didn't want to start. The feeling at that stage was not good - utter helplessness. I got it going and we took off. This creature never moved toward us though. Thank Christ it didn't.
Thinking back on it and examining the situation, the feeling I had at the time was reminiscent of blindly walking into something you shouldn't experience, or standing outside the window of a house where something bad is going down and one of the occupants looks up at you.
To those of you who doubt, you'll know it if you experience it.