This article claims that Celsius and caffeinated drinks can lead to brain fog and can cause symptoms of not getting sleep well or can cause serious low or high blood pressure.
In the Vail article, Dr. Lipton says "Often people don't realize they had brain fog until it clears up" meaning that even when you drink caffeinated drinks on a regular basis you won't know if you have brain fog or not, although when it's treated you "suddenly feel - and think - better". That being said, caffeinated drinks isn't the leading cause of brain fog, leading Dr. Lipton to state "treatment can be as easy as going to bed earlier, sleeping with oxygen (for sleep apnea), consuming less alcohol and caffeine, eating health foods regularly and even drinking more water". This quote is saying that there are other factors that go into having someone get brain fog, not just from caffeinated drinks.
Another interesting fact is an article from Christopher Drake stating "results demonstrated a moderate dose of caffeine at bedtime, 2 hours prior to bedtime, or 6 hours prior to bedtime each have significant effects on sleep disturbance..". This is something that a lot of people may not take into account. No matter if you have a caffeinated drink 2 or 6 hours before you go to bed, it's still going to have the same effect on your sleeping habits, causing insomnia, the need for more caffeine and your hygiene habits.
Although these articles claim that caffeinated drinks cause brain fog and can be treated by sleep, drinking water, and changing your habits, the article by Sara Berg states "In low doses, caffeine may cause depression" which makes a different claim saying that you can have it but not as frequently.
I believe that these articles are exaggerated/misleading due to different articles spinning different claims about how caffeinated drinks cause brain fog.
https://www.vailhealth.org/news/could-it-be-brain-fog
https://pmc.ncbi.nlm.nih.gov/articles/PMC3805807/