The truth to motivation is that not everyday will be perfect. On some days you will be less productive than you want to be. You may find that you have done nothing at all, or are behind where you want to be. This 'bad' morning, afternoon or day does not often mean that you have completely failed. If you hate yourself or sulk following a period of unproductivity then that will often lead to further unproductivity. Don't turn a bad morning into a bad day. A bad day into two bad days, or into a bad week, or a bad week into a bad month.
Instead of criticising yourself for being unproductive, be solution focused. Think only of what you can do to help solve the problem. Ask how you could make a start and build momentum. One technique that you could use is to turn unproductivity on it's head, and aim to 'save the day' (or week, month, etc) by being productive and making life easier for yourself tomorrow. You could make a plan, write down some notes or organise yourself so that tomorrow will not also be a bad day.
This period of unproductivity is an opportunity for you to better understand yourself and how you work. By learning to be resilient and proactive now, you can apply these skills to both reduce how many 'bad days' you have and, where you find yourself being unproductive, to quickly bounce back before it is too late.