Although all travellers seem to have their own opinions on the matter, it can really inconvenience the passenger directly behind you if you put your seat back too far, preventing them from having proper leg room or the space to put down their tray table.
Of course, during overnight flights while most passengers are sleeping, this is more acceptable. If you do put your seat back, it’s always nice to let the person behind you know beforehand to avoid hitting their legs or knocking over anything on their tray table.
Germs are a major issue on planes, as they can spread all too easily. Be aware of the fact that you’re seated extremely close to other passengers, especially if you’re in a middle seat.
If you’re sick and know you’re going to be sneezing a lot, keep a pack of tissues on hand so you’re not getting everyone around you sick. However, if you are really unwell and there’s a risk of passing your sickness onto others, it may be best postponing a trip.
It may well be an inconvenience, but travelling is for the healthy - if you embark on a journey with a bad cough, you’ll most likely fall more ill and get everyone around you sick in the process.