Don't freak. It is good that you will have a brain MRI next week. Will it be with and without contract? The symptoms that you are describing can be consistent with MS however there are a few disease that mimic MS and visa-versa. I have had these symptoms on and off for 8 years and I am able to live a full, productive life with my MS.
If it turns out that you do have MS, there is a great support system within the MS community. You also mention Fibro, that's odd because I was dx'd with Fibro not too long after MS was given. I actually cured my Fibro this year by eating foods that do not cause inflammation & Fibo is an inflammatory disease and inflammation generally begins in the digestive tract and then migrates to the muscles, cells, etc...google his name, Asa Andrew he's wearing blue with a green apple (book).
You state that "I thought that symtpoms were more constant and progressive". MS is a tricky disease. We in the MS community call it MonSter. It shows its ugly head when it wants however there are things that one can do to tame it or even put it to sleep for a while. There are four types of MS. (short version)
RRMS (Relapsing Remitting MS). This is the most common, flares can happen which brings back problems like a heavy leg, stays for a bit and then leaves.
PPMS (Primary Progressive MS). This is where the disease itself progessively gets worse over time.
SPMS (Secondar Progressive MS). Some RRMS patients will become SPMS after 20 plus years. Other patients never leave RRMS status.
Benign MS: A person has MS but it really causes very little or no disruption in the persons life.
If you google MS you would be able to find out all kinds of information regarding this disease along with other disease that mimic such.
I have six lesions on my brain and that was 8 years ago and the MRI that I had last year showed no more (initially I had one every 6 months and then every year thereafter...including my spine). Spinal lesions cause more disability, like loss of walking, etc... So I am thankful that mine are in my noggin.
MS: Unpredictable Disease of the Central Nervous System.
I always loved being spontaneous...however this is not what I meant.
Good luck and keep us posted. If you want to you can PM (private message) me.
Did you ever serve in the military? I have a reason for this question...
~Zig