Is supplicating for death upon oneself – in a moment of anger and satanic whisperings to transgress the prohibition of the Prophet, peace and blessings be upon him – truly a supplication against oneself, or is it a satanic whispering?

It appears that the questioner is afflicted with waswasah (obsessive whispering/doubts). The cure for this condition is to completely ignore the waswasah and to occupy one's time and energy with beneficial activities, such as learning and serving oneself and the community. Envy (hasad) and the evil eye (ayn) can be treated with lawful ruqyah. It is not permissible to supplicate for death upon oneself.