If there is no chemical sanitizer in the water of your Jacuzzi (בריכות ספא), which is to say no bromine or chlorine in the water, then this would allow bacteria levels to grow exponentially in a very short period of time. Getting into the water during this period of time would expose you to a huge amount of bacteria. Depending on how long the water has been without sanitizer the type of bacteria in the water can be hazardous. It is not unheard of for bacteria to become so dangerous that it can be life-threatening in extreme situations. This is why it is critically important to maintain a measurable sanitizer level in the water at all times. If the water does not have one part per million of free chlorine or 2 ppm of bromine then it is not safe to use.
If you suspect that you have follicular dermatitis, or Jacuzzi rash (בריכות ספא), you must to seek professional medical advice. Many forms of this skin bacterial infection will not clear up on its own without the use of a topical or antibiotic treatment. The symptoms may disappear for a period of time. However they are likely to return should you aggravate your skin again, for example by using the Jacuzzi.
Biofilm grows inside the plumbing lines of the Jacuzzi. The biofilm creates a layer of mechanical protection over bacteria in the plumbing lines preventing chemical sanitizer in the water from reaching, and destroy this bacteria. The motion of the water moving through the plumbing lines can sometimes peel some of this biofilm away, however to actually clean it you must use a pipe flush chemical additive in the water. This is usually accomplished by adding a liquid additive to the old Jacuzzi water (ג׳קוזי לחצר) before you drain. You would then run all of your jets on maximum with this chemical in the water and it will remove the biofilm.