Losing 2 of your three dragons and bulk of your army soon after you finally manage to arrive on westeros. Having your claim threatened by what is the greatest and most legitimate cause out of nowhere. Having your closest advisors being killed, switching allegiances. Feeling like theres no one on your council left that's actually loyal to you. Not recieving the same welcome in the norh that you recieved automatically in almost every other place you've barged into with your army. No longer the most looked-up-to. No longer the one with the most power. No longer among others that you vastly outrank(even if you outrank them, the gap isn't as big now). Finally where you wanted to be your entire life but still feel like a stranger here. Realise you'll always be a stranger. Realise that this conquest won't end like the others. Overcome with emotions regarding all the things that happened in this place. No longer having anyone by your side that you trust enough to hold you back like many people did in earlier seasons. Overall, just a mix of insecurity, fear, rage, uncontrolled impulses.

Yeah sure... there have been zero buildup over 8 seasons and this is completely illogical. Clearly, everyone who keep saying that she was impulsive and dangerous before are talking out of their ass, right? If you don't see it, it's because you want want to see it. You were too much into the whole "saviour" sthick and your headcanon to actually realise what her character was doing on screen all this time. Season 8 was heavily rushed. But saying shit like "it's compleletly illogical", "it came out of nowhere", "it was completely unpredictable" is beyond foolish.