When to sleep in same room with ill toddler?

[AlmostCutMyHairToday]

My 2yr 11month DS has come down with a temp of 37.8c, and rapid breathing (28 breaths per min). Blocked nose but no coughing or wheezing. Gave him calpol. He was pretty alert before bed, but I just don't know if I'm meant to keep a close eye on him in case things change quickly in the night. Should I sleep in the same room? But if I'm asleep will I even notice if there's a change?

I'm not even totally sure what to look out for / what's an emergency. I've read that if the breaths per min are over 40 then that's a sign of distress, but is that enough to go to A&E? Or is it fast breathing plus some other symptoms? What would warrant waking him / disturbing his much-needed sleep to take him to A&E?

I really struggle to get any perspective when my DS is ill, I just start to spiral and worry : (

Any tips for health anxiety also appreciated. I really need to start working on this.

Thank you all for the advice, it really helped put things into perspective. He's been fine. Like some PP's have mentioned, I think the more he is ill the more confident I'll become in terms of what is and isn't normal. I guess he's just not been ill very often (not in nursery yet!), so it does throw me.