I see many cockroaches dying at the same time in my house all of a sudden?

all of a sudden, i see many cockroaches dying at the same time in my house.. I am able to see, these cockroaches running or flying crazily and after some time, i see them lying upside down, and dying soon.. I am able to notice this mass death (suicide) all of a sudden all over my house.. I didnt use any pesticide.. WHY?