How do I know if I am lugging?

Didn't really drive a manual car, so I am not familiar with the term.But I was riding around today, cruising in 4th between 40-45mph in the 4-5K RPM range, got it up to about 5.5-6K and decided to put it in in 5th going about 50-52mph and it dropped the RPM back to around 4K.Since I am not familiar with the term and I am new to riding, I'm not sure if I am in too high of a gear with too little RPM for the speed I need/want.I just don't want to damage my engine by being in too high of a gear, and I don't think there is a table anywhere saying what gear at what RPM at what speed range I should be in. via /r/motorcycles https://www.reddit.com/r/motorcycles/comments/d15nw0/how_do_i_know_if_i_am_lugging/?utm_source=ifttt