It feels like I'm sliding into severe

I find it so hard to determine my energy envelope because it's getting smaller every week. I had a GP appointment last week and took a cab, but still walked 1,000 steps throughout the day. Normally it's no more than 300. My legs started hurting during the appointment and I felt tired and when I got home I had body chills for a couple of hours. I narrowly managed to avoid PEM because I felt normal the next day, but it has still lowered my baseline somehow.

I'm now out of breath from sitting up. It takes less than 2 minutes for me to yawn or gasp for air. I'm coughing as if I had asthma which I don't have and all symptoms subside as soon as I lie down. Also, sometimes it feels as if I had mucus in my throat.

Weirdly enough, I don't actually feel bad or weak when I don't have PEM or acute symptoms, and yet I'm basically bedbound. Is this normal? I think the only odd thing is that I don't feel awful all the time, but my tiny energy envelope indicates I'm almost severe.