I always fall asleep fairly quickly, it just doesn't last long.
Like you, I get one 'good' night's sleep every 7 - 10 days, simply because the body just shuts down. I'm not sure it's 'sleep' as much as 'passing out'
'Good' in this instance is defined as over 5 hours of sleep, if I hit 6 hours it's a major milestone.
It's been this way since I was in my teens (40 years, give or take). I'm quite accustomed to it by now, but there are times when I'd REALLY like to know what a full night of sleep would be like...