To backslide, according to Merriam-Webster, is "to lapse morally or in the practice of religion."
Backsliding may mean that we now spend less time studying God's Word or praying. It may mean we meet less often with brothers and sisters in the Lord, or that we look for fewer opportunities to "do good unto all men, especially unto them who are of the household of faith." (Gal. 6:10) Or it may mean we don't try as hard to be "an example of the believers." (I Tim. 4:12) If this is true, we need to identify a cause.
The number of hours spent reading the Bible or serving others is not necessarily an indicator of our dedication to the Lord. At times, job requirements or specific responsibilities can keep us from giving time to Christian activities, and it's not due to lukewarmness. (Remember, that in your workday obligations you can still let your light shine. "Serve wholeheartedly, as if you were serving the Lord, not men."