Halfmoon king betta suddenly died!

[AlexTheGreat]

Its just what the title says its las te and I came into my room hearing my tank making splash noises and i went to check to find my betta swimming iradically then suddenly dieing! He was doing fine no signs of stress or anything. Here are my parameters:

Ph- 7.2-7.6
Ammonia-0
Nitrite-0
Nitrate-10-20ppm
And my tempature was 78.6 F°

Here are some pictures of his body if it helps

 

[Toad]

Maybe something spooked him and he slammed into the glass? Would have explained the splashing noise. I've seen fish die that way.

 

[AlexTheGreat]

That would be on explination although i dont know what might have spooked him