My cat seems afraid of something? And it's affecting me?

So everyday I let my cat go outside in my yard but we tie her up so she doesn't leave and Friday evening she was outside in the shade in the dirt under a bush and suddenly she just ran to the door like crazy and just wanted to go inside like she got afraid of something and started liking herself like washing herself really bad and then she hid under my parent's bed but she never go in my parent's room. The next day she didn't went outside all day so I thought it was time for her to get her outside so I was looking for her but I couldn't find her anywhere so I called her with treats ( this always works) and came out of nowhere so I took her outside and she just ran and hid under a bush and she was so scared but I don't know of what so I took her back inside and she just jumped out of my arms and ran under my sofa and stayed there for 1 hour or 2 and never moved so that's when I started being worried. The same day when I was going to bed she got out of under the sofa and went in my room like she always does and she seemed fine. Then today I got up and she was still sleeping in my bed but I got up with some kind of "illness" on my scalp I guess like if something bit me but couldn't find where it bit me so I went to work and when I came back from work I realized it was beginning to "hurt" other places then my scalp like if something bit me at many places and my arm was itchy and turning red and it felt like it was burning. That day my cat still didn't went outside and seemed like she was still afraid but afraid of everything surrounding her and hid under the sofa and under my parent's bed all day. But in the evening she seemed fine like before as if nothing happened. So I don't know what's up with her but does someone know what could have happened to her while she was relaxing under a bush on a normal sunny day? And do you know if it could have somehow affect me? Or if my itchy skin have nothing to do with my cat? Because I'm getting worried. So yeah I'm sorry if it's a long description lol and I'm sorry if I made any mistake but my main language isn't English so please if you know anything please tell me

First, tying your cat up outside doesn't sound safe.  What if there were a predator or something that tried to get her? I suspect that's what happened.  Maybe she would be happier inside.

It is possible that something bit her and then also bit you, but there is really no way of knowing.  It sounds like you should go to a doctor and maybe your cat should go to a vet.  I hope you're feeling better.

I've never heard of anyone tying a cat in the yard, I would be terrified to do that for the same reasons talkingpeanut discussed above.  A cat could also twist around and choke themselves easily if tied with a collar around their neck that isn't a break-away.

I don't know where you are, but there are quite a few biting/stinging insects that nest in the ground.  It also could be she rubbed against a poisonous plant and then rubbed it on your bedding or something.  I've caught poison oak before from my dog leaning against my leg after he had run through it. 

PLEASE do not tie up your cat.  How frighting that must be to not be able to move around and escape from harm.  Please do not do it.  How about a large cage for outside . . . .anything is better than leaving your cat tied up.  You got to even be careful with an outdoor cage as I have heard of fire ants almost killing a cat left outside in a cage.