I called 911 on a drunk driver a couple months ago. He was drifting over the centerline a few feet and would always over-correct.
Certainly it could have been a distracted driver, drunk, tired, high, heart attack, whatever. Doesn't really matter why because he shouldn't have been on the road, no matter what the cause was. I saw in the newspaper later that he did in fact get charged with DWI instead of DUI but no BAC was listed, so it likely was just medication or something. Regardless, head on collisions at 55+ MPH are no joke. There's a reason crash test ratings are done at 40 MPH. Faster and it's anybodies guess what happens.