How long do you usually meditate for? Perhaps you can experiment with different lengths of meditation at different times. It could also just be that you are in a clearing/releasing phase energetically. All that regular meditation started to release old stagnant energy, leaving you feeling tired as it clears out.
One more idea is do more grounding work, like to exercise more and make sure you're eating healthy. I don't know how long you have been a meditator, but it is common to go through different phases of experience. Don't be afraid that you are stuck in this phase. As they say, this too shall pass.
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