Hard to say the three day mark is usually the worst days of fasting. At least for me. If you’re doing electrolytes and feeling that way then tread cautiously and listen to your body. Is this your first fast or first fast in a while? Your body is producing more cortisol which can raise the heart rate and make you feel winded easier . Maybe take something with you to eat if you are worried but I used to run ten miles fasted and never passed out ever. Gluck
I feel that way sometimes too! I usually run during my fasts and sometimes I need to run at a turtle pace . When Idid my 5 day fast at day 5 I had to take breaks walking because I “needs to rest for just a moment!”
Since it’s your first fat (as was my 5 day one was) you’re still not fat adapted, aka it’s still not used to burning your body fat as fuel.
From what I’ve read fat adaptation is a bit of a learning process for the body and it takes about 4 weeks to become fully fat adapted. Until that time I feel like the body is struggles to accept that the metaphorical car is out of gas and it has to walk for a change.
Once you’re fat adapted (I’m not there yet myself!) and your body automatically knows to switch into fat burning the results are amazing. Apparently endurance athletes have found that being fat adapted allows them to run longer without needing to eat those gels mid run.
Hope this tidbit keeps you going! :)