I’m afraid I cannot offer anything divine, but I can empathize. When I feel tired and sad (like you, I don’t know which causes which or if they just always come as pair), it often comes after a period of restlessness and nervous energy, like a wave crashing. Once it crashes, I catch my breath and brace myself for the cycle to begin again. I must think of these cycles as ocean waves, because they are predictable and even comforting. Tired and sad will always come to an end, so will restlessness, and I will always get my breath. Hold out for that breath! It will get here in time.