I hope she is ok. I haven't tried using a human hot water bottle but can imagine they can be very hot if they don't have a cover, and it's always difficult to know where to put it. I find the snugglesafe one, after it's 7 minutes in the microwave and with it's cover on - is definitely quite warm, but not hot. Having it on top of the cage seemed pretty ineffective - heat rises. Having it directly underneath, could warm the plastic and substrate too much (Coco had a good idea of standing the cage on some books and having a heat pad underneath the gap so it wasn't directly against the cage base).
My cage is quite large so I wanted the snugglesafe at the nesting end. So hung it against the bars there - it leans forward slightly and the bars also give ventilation. I think if it had been too hot there our hammy would have moved his nest elsewhere.
A lot depends on the kind of house you live in possibly and it's warmth level. A draught-free areas is important (good that you moved her
). Where we live is old and cold, no double glazing and the room is hard to keep warm without a low level of heat on day and night in winter. But I found after we moved here that I also needed a blanket on top of our hammie's cage - the sides are still open for ventilation, but even with a level of warmth there can be draughts and cold spots.
In a more modern insulated house it could get too hot with extra heating and a bottle as well - but it sounds like you have it about right. If the bottle is wrapped in a jumper or fleece blanket or something I don't think it would get too hot, the heat would be more gentle and in a certain area. A thermostat usually turns heat off when the room temperature is at 20 degrees too. Our little oil filled heater has a thermostat on - it turns on and off when the room temperature is reached/drops. It's not that exact but kind of works. At first we didn't use the thermostat and the room would be very warm and toasty in the mornings, but if it's a draughty house you have plenty of ventilation! Our hammy seemed to "sunbathe" in his spunik when it was like that!
The main thing is that they have the space to build a large nest. Having a part "subterranean" house in winter can help as well - ie the house part buried in the substrate so the substrate is packed around the outside of the house. And you can even put some on top. You could have a tube or tunnel leading down to the house entrance. Although this works best if the house has a lift off roof (a shoe box house could work like this). Then even if the room isn't that warm they are able to make a cosy space. And that should be enough, unless the temperatures are freezing at night - which they can be quite often in winter, especially early morning - and then a very low level of heat overnight will help.
From what you said about her cage being in a draughty area to begin with it does sound like she may have started to go into a torpor each time, but hopefully it is resolved now. It's bound to make you worried after it happening before as well. But if it is daytime it is normal for them to sleep quite heavily. In the evening I'd be a bit concerned if you couldn't wake her.
I find it very hard to wake our Syrian these days - he doesn't respond to sound at all and I think he has gone a bit deaf (if not totally deaf) in old age. But touching him wakes him up.
If she has recovered now, just try adjusting her cage, amounts of substrate (6" depth if you can) and a big pile of paper nesting material.
But a vet check could also rule out anything else, as Thin Lizzy says, and may give you some reassurance or spot something underlying.