Like others have said, that’s not nearly enough water. I don’t know dehydration alone would cause nausea, but with such a small amount of water combined with salts, you may have basically just swallowed sea water…
Also, many people are sensitive to tea on an empty stomach, so that could be contributing, but I would focus on upping water intake first.
Your stomach only has stomach acid in it and a natural reaction to high levels of stomach acid is nausea/vomiting. The only things you consumed (coffee/tea) are also acidic.
You may want to try getting some of your sodium from sodium bicarbonate instead of sodium chloride. I always keep sodium bicarb tablets on hand. Easy way to get salt in while neutralizing stomach acid and not breaking a fast.
Thank you all for your advice so far :)
I found the water with fasting salts unappetising to drink which is why I struggled to drink enough of it.
I’ll try adding lemon juice/apple cider vinegar in future to make it more appetising.
Will also drink more plain water as recommended.