This happens to everyone. We all have days, even weeks, where our energy levels seem low, and mentally, we just aren't on top form.
The first thing to remember: don't beat yourself up about it. It's perfectly natural. Human beings have lots going on! Your physiology is complex, your emotional life is complex, YOU are complex. So don't worry too much if you're going through a patch where you feel, well, human.
Now, every winter, I go through the same cycle. The cold days and long nights draw in, and my motivation plummets. I find it difficult to get myself out of bed, and the idea of hard physical exercise is enough to make me even less likely to face the day. It's taken me a long time, but I've finally learnt. It's okay that I feel this way. The world isn't going to end if I change my routine to fit the way I'm feeling. My body is telling me that it needs a bit of a break, so that’s what I’ll give it.
That doesn't mean that I sit around all day, devouring Ben and Jerry's Cookie Dough, without doing any kind of exercise. I know I’ll feel rubbish if I do that. It won’t help. What it does mean, is that I take a gentler approach. I don't force myself to do anything. I take some time to consider what it is that is really putting me off exercising that day (sometimes it's as simple as not wanting to get changed because it's cold!), and modify my approach. I don't want to get changed, so I decide to do a light,15 minute yoga stretch that doesn't require a change of clothes. More often than not, by the time the stretch is over, I'm warm and ready to go. Getting changed doesn't seem like such a barrier.
There's no need to fight yourself at any point of your fitness journey. Your body isn't an enemy. It communicates with you, and if you can listen, you'll find the right balance and learn to develop a seamless rhythm and connection with it. Your default should always be kindness and compassion towards yourself, so if you're having a particularly difficult day, or week, slow down, listen to your body, and don't be afraid to change things up. Your body always wants to move, it thrives on exercise and movement, but that doesn't always mean intense, extreme routines. Sometimes, your body will be content with a relaxing stretch and some quality downtime with you!