Low Energy & Feeling Sluggish while on deficit

Hi everybody!

I've been having some issues with energy the last couple of weeks. It first happened about two weeks ago. I had a day where I went pretty low below maintenance level with my calories. Actually more than 1000 below. Since this isn't something I normally do, I didn't think much of it. That same day I did pretty intense cardio.

The day after I was pretty low on energy. I felt sort of sluggish, and I was reluctant to move much (had to work, though). I just figured it was the low calories and the training. So that day I ate more, ending up around 500 calories below maintenance. But the day after that was even worse. Felt even more tired both physically and mentally. Was around 500 below that day as well.

After that it was fine, and I could train after that. But the same thing happened to me again last week, without me going THAT low on calories. What strikes me is that this seem to happen now. I generally feel pretty slow and sluggish. Is my body reacting to my dieting? Is it trying to conserve energy?

I'm a semi-vegetarian, and I eat no red meat but fish a few times a week. I made this change to my diet pretty soon after I starting counting calories. I'm aiming for 55% Carbs, 25 Protein and 20 fats. I feel pretty varied and healthy in my eating habits. I eat a lot of vegetables, beans, berries, nuts/seeds, oats/grains, yogurt/eggs/cottage cheese.

Thanks for any feedback.