Are the mentioned symptoms of heart palpitations, desire to cry, cold extremities, fever, fatigue, and loss of morale, due to disbelief-related whispers, considered symptoms of the evil eye, jinn possession, or sorcery, and what is the cure?

What you are complaining about may be due to the evil eye, jinn possession, a physical illness, or a psychological one, but one should not surrender to these delusions. The cure for what has been mentioned is through the Qur'an, legal ruqyah (exorcism), prayer, and supplication. One can perform ruqyah on oneself using Al-Fatiha, Al-Mu'awwidhat (Surahs Al-Falaq and An-Nas), and prophetic supplications. It is permissible to seek help from the righteous and to consult trustworthy psychiatrists. As for obsessive whispers (waswas), they do not harm as long as you dislike them, and they are a sign of faith. Their cure is through frequent remembrance of Allah, seeking refuge from Satan, and ignoring them.