Early Onset Alzheimer's?

Yesterday I ran one of my normal 4 mile routes. I've been running said route for a solid 1.5 years. However yesterday, I got lost getting home.

Suddenly I looked around and thought to myself, "Huh, this doesn't look familiar." I was so turned around that I actually had to use my iphone maps to get me home.

This is concerning to say the least. This proves my ability to become completely focused on thought alone...but is no excuse for actually getting lost a mile away from my home. I do not know what this says about myself.