My sleep makes me so unreliable

I hate how I can't seem to figure out why I'm staying awake or falling asleep, because it always seems to happen at the worst possible times. I'll wake up long after anyone needs me to actually do stuff, then fall back asleep right before someone needs me to do something else. Last time this happened, I costed myself the only way I could even half-manage to sustain a job, because I'd basically sleep right up until the person showing up to pick me up was actually at my house to pick me up from work. I've been told when I was younger that taking naps is bad because I can never manage to actually "take a 10-20 minute nap" without setting a crazy amount of alarms I don't trust myself to heed.