EOS CPU Resource Limits
The EOS network requires every account to maintain staked resources in order to perform transactions. As the resource needs of the network rise, so do the demands on your staked resources. Particularly the CPU. Your CPU stake determines how many transactions you can make on the EOS network within a certain time frame. Because of the fluid nature of the EOS network, the number of actions you can make on the network will fluctuate.
If you find your CPU resources exhausted, a few Block explorers have made it possible to delegate additional resources to your account for a short period of time.
The fluctuations can differ hour per hour and day by day depending on the demands of the network. As you can see from this image provided by EOSCharge.io CPU Resource Costs are very fluid. This is chart is updated in real time and can be seen here. https://www.eoscharge.io/
You can also add in your EOS account name and see the available resources to your account by percentage available... and how many actions you may take at that time.
and how many actions you may take at that time.
This information can also be viewed in the Advanced Drawer of your EOS wallet.
For a more in-depth explanation about why your account runs out of CPU. Leading BP (Block Producer) EOS Canada has put together a great explainer: