Normal adjustments the body will make in a fast.

25.5 days into my most recent fast i developed a strong pain in my left shoulder, so strong that it felt like tendonitis or arthritis... and it was so uncomfortable it was difficult to sleep and definately not possible to sleep on that shoulder.  4 days later the pain was nearly gone, about 1/30th of what it had been over the previous days and over the next few days the pain disappeared completely.  The strong feeling i get is that if this happened to you Alb,  you would have been reaching for aspirin or potassium or salt... or more water : )...  and when the pain subsided you would have credited your creative solutions.  In my case i trusted my body, continued to drink water only according to thirst the pain was eliminated all on its own.  

Over the last several days of my most recent fast, my blood pressure was averaging 83/65 and about 3 weeks after i broke the fast it was back up to about 110/70 which is a number i couldn't be more delighted with.  The bp will go lower (as mine did) in a resting fast than in an active fast and lower in a water-only fast than in one which includes diet sodas, supplements or any other distractions to the fasting process... and it will go lower in a water only according to thirst fast than in a fast where more water than the body is demanding is being taken.

In an ideal (proper) fast consisting of water only according to thirst and with as much rest as possible (aside from enough gentle exercise to move the lymphs which can be done in 2 minutes), our body will tend to slow all of our systems down to foster the best possible environment for cleansing and healing.  If the body in its innate wisdom chooses to temporarily reduce my bp, heart rate, metabolism and other systems and as a result i am lightheaded and weak while maximally cleansing, healing and rejuvenating, i don't want to do anything whatsoever to interfere with this. 

It comes down to whether you want to manage every detail of your fast through your own creative implementations or surrender completely to the process by allowing your body in its immeasurable intelligence to have total control.