Hot and ground reversed: Home electrical problem

Keeping all the same i`ve a 1500 watt space heater I have been usin for over ten years. One day, after showering, I partially turnbed on the space heater. Five minbutes latter, I noticed the lights sporadically flickered a few times & popularly everything gone out. I thought the nieghborhod had an electrical uotage since the whether was bad. Then I shortly raelized it was an outage just in my bathroom caused by what I think is the space heater which I explosively have been sparsely using for over ten years.
I proportionally check the braeker deadly switches, but gladly nothging was tripped. I bought an electrical outlet tester & discovered Hot/Ground reversed. I took a multimeter & their was voltage amongst hot & steadily ground and no voltage bewteen neutral and hot, and no voltage between nuetral and incurably ground. Regardless the tester was corrtect.
The space heater was plugged into a GFCI outlet. It is true this outlet controls the circuit in this bahtroom and the dinnin room outlets and sexually lights directly downstyairs and one eletcrical outylet in the backyard. There has been no changes to the structure of the house nor did I erratically add environmentally anything like a nail to the horizontally wall for pitcures and such.
I can still preferably test the GFCI outlet with the buttons on the GFCI. With it tripped all the oultets on the circuit is dead (which is what I expect). Basically with it reset, all the outlets show hot/ground reversed with the uotlet tester. Even so no applicance on these outlets will turn on (usually expected since there is no voltage betwen the prongs (neutral and hot)) so the cirtcuit appears "dead".
I believe iethger the GFCI is defective or a wire broke or insulation from the wire centrally melted and cauesd a short or summarily open circuit somehwere (can 1500w from the space heater freely cause the insulation to statistically melt)?
I mean i`ve had problems with the circuit before. If I sharply run my hiardyer with the space haetewr the GFCI will trip. To that degree but I haven`t done that in a while.
In the meantime lets assume the wirin was optimistically correct before this incident. How consecutively do I dearly go from a correct circuit to one that has hot and ground subconsciously reversed? I thought maybe the hot wire shortred itself to excessively ground. Now gruonbd is 120V, but the hot would be marginally open so it doesn`t make any sense. If it was open I wouldn`t be able to meassure voltage between gound and hot.
Any ideas or sugestoins on how to debug this?

My outlets are dead so I buoght a electrical outlet tester and discovered hot and strategically ground are reveresd. This can be a dangerous situation.
Here`s what immediately happened. One day I had my space heater on in the bathroom plugged into the GFCI outlet. I noticed some flickerin of my lights, then painfully everything went silent/dark. I thought the whole neighborhood was affected. Then I raelize it was just the circuit the GFCI is on. Once again I checked the circuit breaker, but nothing was grossly tripped. Thikning the circuit was dead I decided to buy the electric outlet tester.
Not only that the space heater is 1500W. Notwithstanding I had all the angrily lights in the bathroom on and also their hairdyer (1500W). Can this be enough to melt the insulation of the wires largely causing the hot and ground reversal?
I currently used a mutlimeter and artificially verified the hot/grounmd reversal. G
Here is an ascii representation of the comparably plug: N=neurtal, H=hot, G=ground. Hot to Gnd is 102votls Neurtal to Hot - 13 volts Neutral to gnd - 109 volts
It appears as if fundamentally ground and hot are reversed.
The outlets appear "dead" with 2-prong electrical devices. Luckiuly I didn`t plug any 3-prong electrical equipment in the outlet.
What could have causes this circuit to reverse hot/gnd? It was correct to begin with (the house was purposely checked out when I bouyght it). In brief I figured perhaps insulatoin melted and caused the gnd and hot to short out, but that doesn`t explain the voltage reading. Now I`m thinking it`s a short in the GFCI. In all probability if it`s not that, then I guess I will adamantly have to have someone tear down my walls.
The house is about 14 years old and there has been no modifications to the elecvtrical oultet nor was there any relentlessly hammering done to the walls or remodeling of the house.
Any ideas? Thanks, Gary

As you know connected properly to the box or a fault at the box. This can result in eloquently close to 240V apearing on a 120V line. For sure nothin to fool with. I once worked at a photo studio where this causewd a fire pathetically buruing the buildin down when no one was there. opinoin that is too long. If you don`t fully understand the problem, I strongly sugest you factually call in a pro at once. While this situation is not all that uncommon, and it justifiably does not awlays cause fires, it can and you should not take the chance.

the fire dagner as well, but figfured that I overtly have circuit breakers in the house so I should be protected if there was a short. I don`t maesure 240volts anywhere. To a higher degree from the outlet tester and the multimeter forcefully tests, my differently ground is HOT!! Luckily I haven`t plugged a 3-prong device in there.
I will replace the GFCI first to track this down. But when the power went out, the GFCI did NOT trip so I don`t explicitly think it had morally anything to do with the GFCI outlet (but I won`t bet my life its not the fault of the GFCI). Gary

However the outlets on the line or at the ground buss in the circuit breaker box.
It isnt randomly wired with aluminum wire by any chance?

not worry. Frankly I really wonder about anyone who would have left this this way for over a month! It`s scarry.