Hi Diva,
I guess it is very painful emotionally for you at this stage to realise that your dad is getting worse. Perhaps challenging your sad anxious thoughts at this stage may not be the best strategy. What if you when these sad thoughts - tell yourself something like yes I am very sad and anxious as a result right now because of dad's illness. Pause , then ask yourself, what would I like to do about it right now. You will give yourself choices. Perhaps you may feel like crying more, but that is okay as it is your choice for the moment. Or you may feel like this instead -" Okay, I feel really sad but I would like to go out and say watch a movie"
Diva, by getting on with your life, doesn't mean you love your dad any less. Give yourself permission to get on with your life. During times like this, perhaps spend more time with your dad so you will have wonderful memories of him. So perhaps use this time as an opportunity to create more wonderful memories of him. Also when someone you love is gone, though gone physically, your memories of them will always be with you and give you the strength to continue on.
I hope this helps you.
Radha