If being sick and sick day needed:
ASAP (not 5 min before office day starts) inform administrator and team members you are working the most:
the reason;
planned coming back date (so team can plan);
who will be running your tasks (so team members can continue working).
Sick days are understandable as recovery days and:
for Non-EU team: deducted from vacation days;
for EU team: deducted from vacation days or, if "nedarbingumo pažymėjimas" is presented, following the law.
Being sick too often generates unstable work process and upkeeps the team a lot (so team dislikes it).