I have PTSD so feeling some level of anxiety every day is normal for me. It's when it gets overwhelming that I feel like I just shut down.
I had my thyroid checked when I had the ferritin check as well, and that came back as normal (ferritin not normal though).
5k is only about 3 miles in old money. Half an hour's jog, that's all.
Thing is, I'm used to either running every day or going to the gym every day. I can feel I'm missing my weights - I can feel it everywhere in my body. If I'm running on the treadmill at the gym it's 45 minutes. It's great, I can just totally zone out as I'm doing it and I find that really relaxing (for my mind anyway).
Maybe sleeping is a way of zoning out? I really need that non-being time. I find a lot of life quite full on, you know, colours, sounds, people, feelings...it can feel like overload a lot of the time.