I recently went to the doctor to get examined because I have been having trouble breathing (asthma runs in my family). he prescribed an inhaler, but it seemed to make my breathing worse – it felt like my throat was closing up. so I went back to the doctor, and he prescribed prednisone, and it seems to be getting a little better, but even he doesn't know what it is (he said it could possibly be hypervenalation). I'm mostly okay when I am sitting or standing, but when I lay down or try to sleep it gets very hard to breath & it feels like there is something in my throat & i can't get it out, and it kinda feels like my throat is closing up. Are these symptoms of asthma or hypervenalation?

Without seeing you and knowing more history, it sounds more like asthma than hyperventalation.

There are four different levels of asthma. Check the link below.

You might have an allergy to dust mites which could be infesting your entire bed, pillows, blankets, any carpeting and curtains near the bed..
Ask your doctor to have you tested for it.
An allergy can cause asthma symptoms.
If it comes up positive, you need to get a product called (or similar to) Mite Nix, which you have to wash all your bed clothes, curtains, etc. in. You'll also need to get a spray that you have to use on anything you can't throw in the washing machine.
To avoid further infestation, you'll need to buy mattress and pillow protectors that zip over your bedding.
The night after we washed everything in our bedroom, I was able to lay down and not wheeze at all. also, for the first time ever, I woke up without swollen eyes!

It definitely sounds like asthma to me; I experience the same problems when I lie down, and I have had asthma most of my life. It can be hard to get used to an inhaler; if the doctor hasn't given you a spacer, ask him to prescribe one for you. It makes using the inhaler a LOT easier. one of the hallmarks of hyperventilation is that most people experience a bit of tingling in the toes, fingers, and/or lips, so if you're not dealing with that, chances are very good that you have asthma.

I recommend going to see an allergist, as allergies often trigger asthma, and doctors who specialize in allergies are often very knowlegable about treating asthma as well. be persistent, and you CAN get it under control!

I am an Asthmatic and it doesn't sound like you have Asthma at all. to be completely honest it sounds as though you are having panic attacks, which I also have.
If your heart is also racing and you are sweating alot then you might be having some panic attacks, which you should talk to your doctor about.
Otherwise I agree with what others have said, you could possibly be having a reaction to dust mites.
You really need to talk to your doctor about it, and if you feel that they aren't listening to you then you need a second opinion.

I really wish you the best of luck, breathing problems can be really scary.