Earworm in my brain

It’s 1 am, I’ve been in bed for about 2 hours and I can’t sleep. All through my head a song is spinning, over and over: ‘South of the border, down Mexico way…’
On and on it goes:  ‘…That's where I fell in love, where the stars above came out to play..’
And, then (I think there’s a bit missing here, but, who cares?) ‘…The mission bells told me that I mustn't stay - south of the border down Mexico way..’
And then something like ‘..I, yi, yi yiiii., I yii, yii yii….’ But I have no idea if that’s part of the song – probably not – but that’s what’s playing in my head.

Why THIS song?
I didn’t even realise that I knew it!
I certainly don’t like it! I have never purposely played it – either on CD, on-line, from a cassette tape (remember those?) and never on the piano. Nor have I any recollection of hearing it recently on the radio.

Where the hell did it come from?

Any WHY (and HOW?) do I remember the words – and the tune?
And why, oh why is it playing non-stop in my head?
 And at 1 am?

I’d heard that this phenomenon is called an ‘earworm’, so I Googled ‘earworm’ and found that it can also be called "involuntary musical imagery", and "stuck song syndrome".
‘Stuck song syndrome’ describes it well - and that is surely what I had.

Thank goodness ‘South of the border’ is gone from my brain now. I am very grateful - and hope it never returns.

But, but…if I can remember words and music from a song I have never cared about, how is it that sometimes I can’t remember a person’s name, or the name of a place I visited and loved, or a flower I love  - or even just a word?
How come I often can’t remember where I put my specs? Or what’s the number plate on my car?

Memory, you are indeed a strange thing!