Burn the candle at both ends
Definition 1 of 2
Pro Tip 1/3Metaphoric Imagery
Picture a candle with two flames. It's a metaphor for using energy excessively. 
He's surely burning the candle at both ends, studying till dawn and working right after.
Pro Tip 2/3Unsustainable Effort
It implies an effort that cannot be kept up for long without rest. 
She cannot keep burning the candle at both ends; she'll wear herself out.
Pro Tip 3/3Health Implications
It hints at potential negative effects on health from overwork. 
I worry about him burning the candle at both ends; it's not healthy.