Exhausted

So it doesn’t matter how much sleep I get a night, when I’m at work I have moments where I nod off. Usually late afternoon but sometimes earlier. I can usually get up walk it off but the other day I couldn’t fight it and fell asleep and woke myself up snoring. I apologized to my coworkers, got up and moved a little and that was that. Then today my boss, who was gone for the event, says that a few of my coworkers complained that I fell asleep the other day. Like my apology obviously wasn’t good enough, like I have any control over the fact that I passed out sitting at my computer, like it was intentional. So my boss tells me if I’m that tired I need to go home... well excuse me but if I go home every time I’m that tired I wouldn’t come to work. Maybe I’m over emotional but I was so upset by this situation I started crying and couldn’t stop. Am I wrong for feeling like this shouldn’t be a thing, like shouldn’t I get some kind of understanding given being pregnant, it’s not like it happens constantly it was once occasion which honestly is pretty good for as tired as I’ve been. Or am I just plain wrong for letting it happen regardless of my pregnancy being the cause?