Could this be caused by heart disease?

For the last couple of days, I have had several bouts of disorientation, confused thinking, dizzyness. As soon as I lay down, I feel better. I can get back up after 15 minutes, and I'm fine. To give an example, I was sitting at my desk a few minutes ago and had a sudden thought: did I wreck my car coming to work this morning or was that a dream? I went to the parking lot, and sure enough, I had hit a post while driving to work; it barely registered. I'm not drunk or high or anything like that.

It could very well be a heart rhythm problem and YES I would go get it checked out.
You MAY be experiencing atrial fibrillation with a slow ventricular response. and thus decreasing the cardiac output and starving your brain for oxygen by the lack of adequate blood pressure and supply.

Basically you can't pump enough blood to your head.
when you lay down your heart can manage but when you are standing not so well

Dont Sweat It my dear... it doesnt sound like a heart disease to me or have you ever been diagnosed something familiar? You work at a desk... so im assuming you have lots of work and always indoors? IF SO, this might be stress..! honestly, try to figure this out have you been stressing in your personal life? work? (maybe its been going on for a long time) if you have then i know stress makes you feel dizzy, and confused... because it doesnt allow you to have the strong mentality and it makes you feel tired. if thats the case you will need to try meditating and spending at least 30 minutes out at the park to clear your mind. just go for a walk or just sit out there read a book or magazine (as long as your out at a park). doctors recommend 30 minutes a day outdoors to avoid stress and trust me even if your stressing this will help you tremendously. also visit www.webmd.com and find out more about stress, and heart diseases (they also have quiz's that will let you know if you need to see a doctor).
good luck! and lets hope its not something big.. hope you have a good day!
killa mentality
Get to the doctor NOW, and don't drive yourself. This could be caused by any number of things. You may be having seizures. Whatever is happening, you CANNOT be driving...you could kill someone.

PLEEEEEASE, for your own safety and that of others, go to a doctor now....don't wait.

Best of luck.
Doesnt seem like heart disease. But its more like TIA attack. Consult your physician anyway.
Seizures could be the cause, also low blood pressure