What is the ruling on severe oaths like: "O Lord, take my sight," "O Lord, cast me out of Your mercy," and "May God's wrath befall me," for the purpose of adhering to a diet, and are there any consequences if they are not fulfilled?

What you are doing by supplicating against yourself is a grave mistake, for the Prophet, peace and blessings be upon him, said: "Do not supplicate against yourselves, nor supplicate against your children, nor supplicate against your wealth, lest you coincide with an hour from Allah in which a gift is requested, and He responds to you."

You must repent to Allah for this action.

If you have sworn repeated oaths on different things, you owe an expiation for each oath you broke. However, if the repeated oaths were on one thing and you did not expiate, then a single expiation is required of you.

The expiation for an oath is: feeding ten poor persons, or clothing them, or freeing a slave. If you cannot find any of these, then you must fast for three consecutive days, which is more cautious.