Dream about becoming thin is a sign for a need for cleansing. You may be in the middle of some situation that you cannot get out of. Your idealistic notions are deteriorating or being shattered apart. This points to a lack of emotional connection with your father. You need to rid yourself of the negativity and things that are weighing you down.
Becoming thin dream is a hint for a wish to have a current situation or relationship remain the same as it is now. You will suffer some sort of loss in your life. You are not letting others see your true colors. This dream is a symbol for a fear of losing power. You feel that time is running out for you and that will not be able to meet your goals by a set time.
If you dreamt about becoming thin:
Rather than having just one major relationship at the moment, you seem to be working on a number of them all at once. There is plenty of room to experiment and find out which ones are really suited to your true nature. You may come to some conclusions, but it may still benefit you to keep an open mind for a while longer.