My 6 year old daughter has ADD. She does not have any of the symptoms you have. Her doctor described ADD as not being able to focus on anything for any amount of time. If I was you I would talk to a neurologist. You may need to get an EEG or CAT scan, I think they would show anything that may be wrong. Sounds like there may be a blockage or misfiring in the brain. Good luck on what ever you do. I know it frustrating not being yourself.
Ok if ADD is 'defined' by lack of focus - that's what many of my symptoms are. I may not be screaming running like kids do all over the place, but I do "daydream" OFTEN without actually having a dream/imagining something. The fact I'm losing interest/focus in my own sentences when they're leaving my mouth is disturbing. I worded it the way I did because it's not a conscious effort, I really can't seem to "get the energy" to finish - aka focus.
I am either not able to focus (I stare off into space, wander around, or stare at the TV for hours only to "snap out of it" later wondering where I spent all that time. I also lose my place reading almost every other sentence, give up on projects, etc.)
Or I "hyper" focus, especially when I'm drawing, where the slightest interference is the equivalent to nails on a chalkboard and I snap at people to leave me alone. Nothing else matters, I've worked on art for HOURS ignoring my own need for food or bathroom.
Then there's the I can actually function time, which is getting less and less.
Thinking back, I don't know how I got through school considering I would read so far ahead of the class I'd wait a day for them to catch up, but then spend the rest of the class staring off into space. I still get that feeling but when I'm not focused I tend to be just calmly not paying attention to anything. Though I do wander on occasion and I guess that counts as being restless, sometimes I get frustrated with being bored and I fidget.
I had seen a therapist for years that suggested it could be ADD, though nothing more diagnostic was done. I think a neurologist would be the way to go. As for misfiring in the brain I don't doubt it, as that seems to be the case with my mother's mental instabilities.
ADD is usually something that kids are diagnosed with so they can be given grade improving stimulants. Since you seem to have "caught" your symptoms, and they are getting worse it is probably not ADD (a stimulant treated disorder).
An Arnold-Chiari Malformation is more likely given your symptoms. You really need to see a specialist to get it straightened out --doctors, even neurologists, sometimes only know about 10% of their field so you're pretty much screwed if you can't research, lol. Who knows, maybe you're lucky and it will be ACM or something similar (and thus a meeting with a neurologist who specializes in ACM will be able to help figure things out). ACM is treatable btw.
Ok, let me add my 2 cents. I really don't think its ADHD. Something is dragging you down, and it is getting worse. High stress or anxiety can explain a lot of the problems, but not all of them. You have never mentioned if you have tried any medication for stress or anxiety. It's also a good chance its a physical problem. The body aches and pains sounds like Lupus or several other things. It is very possible that the overwhelming physical problems are starting to affect your mental well being. I know that it would certainly drag me down.
What to do? Try copying all you have written and post it in several of the medical sections on this forum. Spend the money if you have to - its cheap compared to the alternative. I would also be tempted to do a complete blood workup/physical to rule out any problems that might show. Although the mind can do a lot of nasty stuff to the body, I don't think a therapist is the way to go. Although I must admit that if you are extremely stressed out, a lot of your symptoms would make sense.
For the short term, my only suggestion (if you are not already doing it) is to get outside. Take long jogs, or walks. Put your favorite music on and walk for an hour. Do something different - go to a zoo, a musical, the movies, your local high school production. Change your routine!
Good Luck!! Let us know whats happening.
Here is an interesting link to what stress can do to memory.
Oops, wiki doesn't articulate the symptoms very well there.
"One of the most common symptoms... is a headache. The headache generally begins in the neck or base of the skull and may radiate through the back of the head." (your headache sounds like one of these kinds)
"Patients may also report tingling, burning, numbness, or pins and needles. Balance can be affected" (your shooting pain perhaps)
Cognatively... the symptoms vary wildly between patient.
" lose the ability to find the right word or to properly form the right word" (this is very common of the condition)
Your mind "droping" sentences is a symptom that I notice in myself. I believe it relates to short term memory problems.
Your daydreams I can relate to, and sometimes after I snap out of it I can't remember what I was thinking about. I think that's because of the short term memory problems again, and that I was thinking about something but I just lose them.
To investigate the matter with out having to spend tons on an MRI you can see if:
-Do any of your symptoms get worse depending on the possition of your head or your posture?
-Does a cool compress at the back of the head help?
-Does getting up and moving about for a short time alleviate any of the cognitive symptoms?