The Code of Canon Law states:
On Sundays and other holy days of obligation, the faithful are obliged to assist at Mass. They are also to abstain from such work or business that would inhibit the worship to be given to God, the joy proper to the Lord’s Day, or the due relaxation of mind and body (canon 1247).
The Catechism of the Catholic Church reiterates this precept of the Church (CCC 2180), with a proviso:
The Sunday Eucharist is the foundation and confirmation of all Christian practice. For this reason the faithful are obliged to participate in the Eucharist on days of obligation, unless excused for a serious reason (for example, illness, the care of infants) or dispensed by their own pastor. Those who deliberately fail in this obligation commit a grave sin (CCC 2181, emphasis added).
People are usually confused as to what “serious reason” might mean in practical contexts. We are considering sickness here, if you have any more concerns we recommend you speak with your parish priest.
Each person’s conscience has a role to play in determining what constitutes “serious reason”. However, the general notion is that one is down with a serious sickness that somehow makes them incapable of going for Mass or of participating actively in it. Each person is to judge his own case to know if their sickness is one that can be classified as serious or not. No one should look at another person’s actions but must judge their own cases separately or consult another trusted Catholic for counsel.
There are some sicknesses that are contagious for instance; you cannot, for the sake of charity come to Church since you might pose a health risk to those around you. Also if you might discomfort or seriously distract those around you with your ailment, you might also consider staying back home.
It is important that a Catholic does not in his heart desire to stay away from Mass on a Sunday or day of obligation but has no choice than to do so for the sake of charity, health etc.
So to repeat, you must consider health and charity when making this decision. If you are going to inconvenience those around you by constantly blowing your nose, or wiping some body fluids regularly while at mass. It is also important to consider if you would be able to sit through the Mass or if you’d be needing to visit the toilet regularly or not, if you absolutely need to lie down and rest.
There are people whose consciences would still not rest even with all the reassurances that it wouldn’t be sinful to stay home when sick. Such people as these might be convinced that if they can lift themselves at all then they must attend. This isn’t really bad, however they need to be sure they’re not contagious. If they are and still want to go anyway, they are required by charity to be sure not to pose a risk to others. They must sit at the end of the pew, avoid physical contact with anyone, and if necessary tell those around them so they’d understand. Do not drink the blood of Christ since you might contaminate the chalice; it is enough to receive the consecrated host alone.