My girlfriend of over 2 years and 5 months has suddenly began to have different feelings about me. She does not know why she doesn't and wishes that things were normal again. Sadly about 4 days ago she said we need to take a break to try to fix this. I'm scared beyond belief that she won't come back to me. I love her with all of my heart and I just want her back. So please help me fix this.

Serious committed couples, in a solid relationship, don't part- or take a break- to try to fix things. Maybe some time alone to cool off, think things over, but an undefined break is, in my opinion, a way out of the relationship.

It's sad that if this is the case, that she didn't have an honest enough character to just tell you straight up, instead of stringing you along, putting you in the position of agonizing over what will, or won't happen. It is cowardly.

Talking is the only way to know what's going on. She's in or she's out, and I wouldn't advise you to hang around like a lost puppy, waiting to see if she'll throw you a bone. Tell her some time apart is okay, a day or two, but if you don't hear from her within a few days, you'll assume the relationship is over.

A break seldom fixes things, it is a break up and they don't get back together. Sometimes they do, but seldom.

A couple go to counseling, talk and find out why they have trouble

You don't fix someone else's feelings, you cope with your own and accept it as a rather nice way to break up. Sucks to be dumped but eventually you grow beyond this temporary hurt and disappointment, and move to better things.

Of course you can't see that now, that's normal, but you will. We all do.

If she truly wished that things were the way they were, she would talk about it, or she'd get counseling, or she'd ask you for couples counseling. The fact that she didn't strongly suggests that she just wants out but isn't angry or bitter and can't be mean to you. You can ask her about the above, but I think it's too late. She isn't getting what she wants from you. Or she has had a hint of something else.
A common reason for a woman is a sense that her man is no where near to talking marriage, children, a home - basically, the future. Women have clocks, don't forget. Another is that her man is treating her like his mother, expecting her to do all the domestic things, and if both work, that can be a death knell. The list goes on, of course.

You are looking at this incorrectly. You don't fix a break. You break to fix a bad relationship. In this case she wasn't happy for whatever the reason might be and decided it would be better to be apart than together. Give her the space she wants, after all, if you don't you are putting the nails on your own coffin in regards to this relationship, if you do, there is a small (very small) possibility she may come back. However, I would recommend to treat this as a full break up and move on with your life.