Stray biting tail/leg, followed by convulsions and drooling.

I started feeding a girl tabby/calico cat a year and a half ago. She showed up after I put food my cat didn't want outside. She was really fat at the time. Now she's skinnier (not super super skinny, probably the weight she's meant to be at) but two weeks ago she finally came up to me and let me pet her. She's now pretty much living in my yard/on my deck. She's extremely friendly and is a lap cat, she was definitely a pet at some point. She's probably 2 or 3 years old.

She bites at the tip of her tail a lot. From what I can see there's nothing actually wrong with it? She randomly will bite at her leg or tail and gets suddenly totally tense, then her body starts freaking out. Today this happened while she was sitting on the bench, she fell off the bench and her body hit my deck (luckily it's a short bench) when she landed she was completely stiff, then went into convulsions. When they stopped she sat still and drool was coming out of her mouth. After a couple minutes she was fine. 

I ordered flea medicine for her because I thought the itching was probably from fleas. Could she be freaking out from bites? Everytime it happens it seems like something suddenly bit her (judging from her reaction). I'm not at the point where I can take her to a vet (plus I am unemployed right now) or anywhere but I'm worried about her. She only likes me when I have food for her and I'm on my deck. 

My cat died last year after having a massive seizure. It was similar to what this cat has, but my cat never recovered from hers and died the next morning. 

Anyone have any idea what could be wrong?

It sounds a bit like epilepsy to me. The seizures can be pretty frightening and can be dangerous (falling off things, predators getting them when they are defenseless, etc.). As soon as you possibly can, get her to the vet. They may have medication for her.

She may have lost weight because she was on her own and with the seizures, she may not be eating as much. I surely hope someone hasn't lost her (or worse, abandoned her). Can you try posting info about her - if the original owners are looking for her, they may see the flyer.

Also, is there a rescue that might be able to help you? Special needs kitties like this one often get a lot of attention and support from rescues and shelters.

You live near me! I'm in Salem County NJ closer to Vineland though- like 15 minutes away. I'm a volunteer as CCSPCA and am going to ask someone there about it when I go in on Monday. I also have heard of "Maddie and Friends". If I can get a picture I'll post on the "lost and found" but she's been at my house for almost 2 years now and I've been keeping an eye out for any lost kitties resembling her. She is super lovable now that she trusts me so I should be able to get a picture. 

I looked up epilepsy and it was definitely a seizure and the website was pretty much describing her. There's a list of what can cause a seizure and with her it could be any one of them because she's outside and I don't know if she has ever been to a vet -.- 

Well, we are neighbors! Maddie and Friends is a wonderful organization.

Hopefully, someone at the SPCA can help. She sounds like she may need medical attention.