Really my question is not difficult but I want to tell you the exact situation in order to see the whole story Inshaa Allaah. My question is about Nathr.
Recently, my mother got ill, and this matter really worried me a lot, while we were waiting for the results of the diagnosis, I thought (and thoughts usually come to me while I am praying, to distract me and make me angry), that I will not watch TV so that my mother recovers (of course that was wrong understanding from me, because nothing will stop fate), and I kept thinking about that Nathr a lot, sometimes to do it, and other times that I’d better not make it because I will not be able to fulfill it, and I thought that what I can do is to try as much as possible not to watch anything that displeases Allah, and that I should better make Du'aa better than the Nathr of not watching TV at all), anyway the next day or something, I got afraid that I might have made a Nathr of not watching TV, I really don’t remember what I said or decided on the previous day. I am really afraid that I might have actually made this Nathr, and because I can not fulfill this Nathr all the time, because it happens that sometimes all my family are watching TV, so I sit with them. Or in general I like watching some programs or certain types of films (I try to choose carefully Inshaa Allaah what I watch). I am really tired of thinking, and I don’t know what to do, what if I really made that Nathr, what shall I do if I can't fulfill it? I really don't want to displease Allaah, but not watching TV at all is something not easy for me to do. Please advice me, what shall I do, how can I ask Allah's forgiveness in case I cannot fulfill this Nathr if I really made it, because I heard that if one made a Nathr, he must fulfill it. (No other way) thinking about Nathr consumes so much of my time, that nowadays I think of Nathr of not doing many of the things I like, like reading books and stories.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

First of all, you may consult our Fatwa: 84494 about watching TV.

As for Nathr (making a vow) the mere thinking about it is not considered Nathr.  The Prophet said: "Allaah has forgiven for my nation for what they think about, unless they do it or talk about it." [Al-Bukhari and Abu Daawood]

So, merely thinking about doing something or leaving it does not make it a vow and the person does not, then, have to fulfil it unless it is something obligatory in the first place; in such case he should do it regardless.  Now, if the person doubts whether he has vowed or not, he does not have to consider that as a vow and does not have to fulfill it because before this doubt a person is certain that he had not vowed and this certainty is not removed by doubts.

However, if you actually vowed then you must fulfill it, if it is a vow of performing an obedience such as praying, fasting or reading the Quran.  But vowing to perform something permissible does not have to be fulfilled, such as not watching TV if what is watched lawful.

As for vowing to refrain from something you like such as reading books, then a Muslim should only leave that which Allaah has forbidden to him.  He/she is not supposed to vow to do more than that, above all vowing is dislikable in the first place.  Imaam Muslim reported that Ibn 'Umar said: "The Prophet warned against vowing and said that it only extracts something from the stingy people." 

Allaah Knows best.