Am I sabotaging myself?

The obvious disadvantage of being an overthinker is that you just can't stop those thoughts from running around. The more you read, the more you explore, and the more thoughts and questions appear.
Despite knowing what I want and where I'm heading I'm continuously having the "What ifs" in the forefront. As much I'd like to think of myself as a strong person and as much as I tap myself on the shoulder for how far I've came, there the moments in life which take me "by surprise" and then it feels like I'm back to square zero.
I've come a very long way coping with my chronical disease and standing up for what I need. Or at least I've thought so till today. My pain came back in a very unexpected time and moment and that threw me back into the "What if" mindset and overthinking my situation and circumstances. As much as I've been trying to put my act together throughout the whole day I wouldn't say I've been successful. And in this state of mind is when I go back to old patterns of questioning myself. The more the logical part of me is telling me "don't go there", the more the emotional part goes in that exact direction.
The uncertainty and disappointment of things not happening the way I plan or imagine them to happen, starts a rollercoaster of emotions and an internal battle. I haven't yet found the reason of why nor how to cope with it. As strong as I might perceived to be sometimes I feel it's "me against me". And I can't stop but wonder whether it's not those moments and situations when I sabotage myself and my happiness because I can't embrace the two opposites "living within me".....