If you truly had no earned or unearned income in 2018, you are not required to file a tax return. That's as easy as it can be.
Please review your circumstances to be sure that you actually had no reportable income. While you took a break from your usual occupation, did you sell any goods or provide any services for which you were paid? If you had $400 or more in self-employment income, you must file so that you can pay self-employment tax (Social Security and Medicare), which is assessed at 15.3%.
If you had interest, dividend, or rental income, you may have enough income to be required to file, even though you were not actively at work.
For more information, please refer to: IRS Pub. 17 Your Federal Income
Tax