Fasting Ramadan is one of the pillars of Islam. Al-Bukhari and Muslim narrated that Ibn ‘Umar (may Allah be pleased with him) said: “The Messenger of Allah (peace and blessings of Allah be upon him) said: ‘Islam has been built on five (pillars): the testimony that there is no one worthy of worship but Allah and that Muhammad is the Messenger of Allah; establishing prayer; paying zaka; fasting Ramadan, and performing Pilgrimage to the House (the Ka’bah).”
Therefore, whoever does not fast Ramadan has abandoned one of the pillars of Islam and has committed a grave major sin. Al-Dhahabi (may Allah have mercy on him) said in his book Al-Kaba’ir: “The believers are unanimously agreed that whoever forsakes Ramadan fasting when he or she is not sick and has no other excuse for that is worse than an adulterer or one who is addicted to alcohol.”
Therefore, a person suffering from anxiety is not exempted from fasting.
On this, Dr. Rajab Abu Mleeh states;
“Anxiety is not a valid excuse for avoiding fasting, simply because it is not included in the legal excuses for avoidance of fasting. It is rather a general term that cannot be determined by clear-cut rules to rely on. Everyone goes through anxiety throughout day and night; I intend here the normal anxiety. However, if anxiety turned to be a disease which makes a person loses his mind and recognition, in this case, it is an excuse to break fasting because a person in this case is regarded as insane and is not eligible then to afford obligations.”
As for missing some days of Ramadan due to studying, a Muslim should try his or her best to observe fasting. The fact that a person is studying is not a valid excuse for skipping fast unless he or she is suffering from health complications or he or she is one of those who are exempted from fasting: the sick, the elderly, the travelers, women in menstruation or undergoing the postpartum period of bleeding; women who are pregnant or nursing their infants.
Students throughout the ages have been studying while fasting without any problem. Therefore, study alone cannot be used as an excuse for skipping fast.
So, if a person misses some days of fast without a legal justification, then he or she should repent to Allah and make up for the missed fast-days after Ramadan.