What if my Depression Is Related to Physical Brain Trauma or Illness?

I am scheduled to undergo a C.A.T. scan of my brain(?) head(?) this Wednesday. I am having some strange problems along with my depression that are worrying me. I am concerned that concussions and head traumas I endured earlier in life may be responsible for both my ongoing, refractory depression and my recent concerns. Here is what I am experiencing:

1) Extreme word retrieval problems. Throughout the day, and almost every time I talk with someone I will go to say something and I cannot find the word or the thing. It is always a simple words I cannot find.

For example, in my session three weeks ago I was describing my learning blues guitar techniques and then how the teacher and I would play together, each listening to the other and making up music that went with the other's playing. There is a word for this. it is simple. As soon as I described it Dr. X. said the word. When I got home it was gone again. After a week of thinking about it it finally came to me a few days ago, and now, for the past 4 days I cannot find the word, even if I try concentrating on the definition for a long period of time. (it is not "accompaniment, or duo, or duet...but something that expresses the making up of the music as you go along...if you think you know the word PLEASE share it with me...it's driving me mad)

2) Confusion/concentration/memory problems.
I feel a sense of being elsewhere (not dissociation) but confused easily by directions, where I am in my car, driving etc. I feel like I cannot stay on task for any length of time, my mind is constantly wandering from thing to thing. I put things down and can't find them a few minutes later. I walk into a room and cannot remember why I am there. I am putting things in strange places. The other day I was looking for the disinfectant wipes I keep on the kitchen counter. I had just used them. I looked everywhere; cupboards, bathroom, other room in the house..then 2 hours later I found them in the fridge of all places.

3) Saying strange things/speaking strangely.
Examples:

• My husband asked me why I wasn't watching T.V. I wanted to say "It's a commercial", instead what came out of my mouth was "It's a nude"...it was disconcerting.
• Then that same day I tried to say something and I started to speak, but it came out as a stutter. I couldn't get it out. I've never stuttered before in my life.
• Then last night I went to say "Turn it down" (the T.V.), but what came out was "make it soft."...which is sort of similar, but not what I meant to say....it's like my brain is shuffling my words.

4) I am tripping and falling and bumping into things much more than usual.

I have fallen and hurt myself 3 times in the past two weeks, before that I almost fell through our front window and about a month and a half ago I fell all the way down my sister's staircase. I am tripping all the time.

On Thursday I told Dr. X about all the head injuries I have had. I am pretty sure I told him before, but he said I hadn't. I have had two confirmed concussions (once at 5 or 6) when I fell from a 12 step stair landing headfirst onto the pavement below, and then at 17 when I was in a really bad car accident.

Over and above that I have had to have stitches due to head injuries twice, once at 16 when I dove into the pool and hit my head on the lifeguard chair's diving ramp and the other when I fell headfirst off my bicycle. I hit my head on the side of the pool in a diving accident. I fell at the pool at the top of the water slide and knocked myself out for a few seconds; I incurred a compression fracture in my spine in that fall, I was bucked of a horse into the hole we had dug to build our new house, again landing head and arm first...and the last one I remember was rollerblading for the first time (and of course being an idiot with no helmet...my feet went straight out from under me and I landed back of head first on the pavement. I ha a massive egg shaped swelling where I landed.

Anyways, I started thinking, what if my depression is caused by an undiagnosed brain injury. Does medication help if it is a brain injury that leads to mood disorders? (I know that can happen because the girl I was in the car accident with had severe mood changes and personality changes following the accident). I also am worried the problems I am having might indicate an illness above and beyond my depression.