I feel a deep sense of dread and I don't understand why

I’m really sorry you’re feeling this , that heavy dread and nausea can be so scary, especially when there’s no clear reason. You’re not alone. If it helps, try slowing your breathing: in for 4, hold 4, out for 6 , just a few rounds can help your body settle a bit. Lean on us, okay? We’re here for you. Whatever you’re feeling right now is valid. Take it one moment at a time.

Maybe something subconscious... especially people get anxious on Sundays before the week starts. I try to remember my favorite quote by author Byron Katie when I'm very nervous.
"Nothing is true".

Sending you positive vibes to take those feelings away from you bro.

I hope the feeling subsides for you soon.