Time to relax and unwind... to recuperate and rejuvenate. Whether from work, an exciting project, exercise, watching calories, or any number of things you might currently be doing in your life... you need to have some down time from it. Your body and mind require a break to keep functioning optimally.
There are two ways to go about taking time off: scheduled and unscheduled. Neither way is right or wrong, so do whichever works best for you.
Some people like routines and like to plan ahead when they will take time off. If this is you, then schedule your breaks ahead of time, and do so at regular intervals. Just make sure you actually do take time off, as it is easy for planners to fill their time with everything else that seems more important (especially when we are focused on achieving goals).
Others like to just keep on going until they feel they need a break. For this way to work well, you need to be good at listening to your body, because you are relying on your body to let you know when it needs a break. If you ignore it, you will suffer the consequences. Burnout is a big consequence if you ignore your body too much for too long. You also need to be able to tell the difference of when you truly need a break, or whether it is just laziness of mind or body trying to let you off the hook of doing what you should be doing. Listening to your body is a great way to operate, but it does take a keen sense of reading your body's signs well. This gets better with practice.
Because my circumstances fluctuate quite a bit, I tend to do a combination of both scheduled and unscheduled breaks, using whichever works best for me at the time. I like to plan, but I also listen to what my body is telling me. Because I've been listening to my body long enough, I can usually have an idea ahead of time when I will be needing a break, so I can usually work it into my schedule. But sometimes I can have a tendency to overplan things, so my body will say, "Hey! I need a break now!" And sometimes a "break" is just mixing up what I am doing by alternating physical work with mind work. One gives the body a break, and the other gives the mind a break.
So yes... go strong and give it your all. Just be sure to take a break every now and then. Your mind and body will thank you for it. And then be sure you don't fall prey to taking too long of a break by not getting back at it again. It's all about balance. After all... it's a little vacation... not retirement. ;)