Or is it? Because you know there are other ways, right?
But that's for another time. Right now, here's some really good advice about how to deal with that overwhelming workload that you've got right here, right now:
Stand-out advice amongst many great pieces of advice:
"Give your boss as much advance notice as possible that you’ll need an extension, and briefly explain why."
Your boss can't help you, manage expectations of others, or stop people piling more work on you, if they don't know you're having problems. (That doesn't mean your boss will do any of that, you might just have a crappy boss. But that's also for another time.)
We'll come back to preventing overload at a later date, because there's lots to be said about email/task/time management, saying No, to-do lists, personal productivity, efficiency, staying motivated, prioritisation, planning, building habits, changing your perspective and a ton of other things that can stop you getting so overwhelmed. For now: read the article, take a deep breath and remember that unless you *actually* save lives for a living, nothing you do is that critical that a little delay will kill someone. So don't worry too much :-)