I don't really think there's anything to worry about. I've taken a course on alzheimer's and one thing you have to find out, is if anyone else in your family has had alzheimer's before the age of 55 (that is very important in your research). There are 2 different types of alzheimer's, one is hereditary (the onset is before 55, but very, very, very, very rarely at your age). The other type, is not hereditary and the onset is later in life, usually late 70's early 80's.
I suffer the same problem as you quite frequently and i'm 27. The reason for my mix ups are because like you said, i'm speaking before i'm thinking. Other times it's because i'm thinking of waaaay too many things at once. You say you're getting ready to move, that could be causing a lot of stress which would make you mix your words up more than usual. I also get lost in mid sentence as well and then totally forget what I was talking about until someone triggers my memory. I got a little worried at one point too but I realized something...If there's distractions, then i'm more than likely to get "lost" on what i'm saying. I've learned to turn the tv down, music down, and shut out background noise before I speak and really think about what i'm saying. I bet if you become aware of your surroundings when you mix up your words and forget what you're saying, you'll realize that something else distracted you.
One other thing that might put your mind at ease about alzheimer's is this: if you had the disease, you wouldn't even be aware at all that you mixed up your words or that you forgot what you were saying. Thus the reason that people with alzheimer's repeat what they say may times over. It affects their short term memory. Thus the reason they live in the past most of the time. Some even need their mirrors removed out of their homes because they don't recognize the person they see in the mirror anymore and it scares them. So with that information, you need not worry and if you have any other questions, feel free to ask. Hope this helps.