Opportunistic infections (OIs) are infections that occur more frequently and are more severe in individuals with weakened immune systems, including people with HIV.
Being nostalgic means to miss the past time. It seems that a real life was in the past because now in the present is different, probably things changed and we know that never is going to be the same. It leads to a nostalgic feeling.
A physical sensation is a feeling. When you sit on your foot so long that it falls asleep, you'll first have no feeling in it, and then you'll have a terrible pins and needles feeling. An intuitive sense about something can also be called a feeling. Your bad feeling about the field trip is justified when another kid throws up on you while riding the roller coaster. A vague sense or belief can also be referred to as a feeling.