Retest ASAP for ammonia & nitrites. If your ammonia is correct at 5.0 then you must do a 50%-60% water change right away followed up by every other day a change of 25%-30% until readings reach 0%. if you cant or are not sure about if the retest is correct do the water change for safety. ammonia will result in blindness,breathing problems and death very quickly at these levels if left. I would stop feeding too, or give very little until you are back on track with your water condition.
can you remind us on your tank size,fish & size, & filter. any maintenance you carry out would help too.
water changes,
how often & how much.
how you clean your filter.
how long you have been setup.