When You're On Vacation, Be On Vacation
This goes for being home sick, being on parental leave, or any other situation where you are officially "not at work".
For many people it can be hard to fully disconnect when you are taking time off. With Slack and email and other things always there, it can be tempting to "check in" or answer a quick message. Often then comes from the well meaning motivation to be helpful to your coworkers.
But when you're taking time off, you should fully take time off. Time off is valuable. It helps you recharge and give focus to parts of your life outside of work. It's an important tool against burn out and something your are entitled to as an employee. Mostly away from work is not the same as fully away from work.
Also, it is good for an organization to learn to work around bottlenecks. If things grind to a halt because you aren't checking Slack for a few days, that is a bug in the system and should be fixed. Any organization that cannot function well with one person missing is not a healthy organization. By being truly unavailable, you help the organization discover and correct these points of failure.
Never feel guilty for taking off time that is yours. Being truly on vacation when you're on vacation is ultimately best for you and the organization.