Hello and thanks for your question.
Ivana, I'm sorry for your symptoms and most especially for your crying as of late. As to why you are getting headaches and why you are more lethargic and more sluggish in your thinking associated with your crying, I cannot definitively say. These symptoms sound very consistent with a depressive episode, which would explain the mood changes as well.
As to why your vision weakens after you cry, this is a straight-forward problem. Your eyes naturally are coated with a layer of tears on the front of them. This enables the front of the eye to be healthy but also allows for clear vision. The interface between this tear film and the air is what accounts for the majority of the refractive (focusing) power of the eyes. When you cry, this tear film is drastically changed with the flood of tears, which are not just water, but also include mucus as well. This can cause a change in the vision because of the change in the tear film composition and volume. Everybody is different when it comes to how long it takes their tear film to settle down. For some it returns to normal within minutes, but for some people it can take much longer.
Just know that these changes are normal and do not represent anything permanently wrong with your vision, as long as your vision does return to its baseline. However, I would recommend that you talk to your primary care doctor about these possible depressive symptoms.
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My opinion is solely informative and does not constitute a formal medical opinion or recommendation. For a formal medical opinion and/or recommendation you must be examined by your doctor.