No, that's not a typo. Aloneliness, unsurprisingly to me at least, is a thing — it's the negative emotions that come from not spending enough time alone.
As social beings, people depend on having other people around them to interact and connect with to avoid becoming lonely, another, much researched psychological phenomenon.
But some people, more than others, need regular spans of solitude to feel mentally balanced and re-energized, to avoid stress and, eventually, depression.
From the Psychology Today article:
The researchers recommended deliberately planning or scheduling time alone in order to avoid what they call a "negative degenerative cycle." They explained that when your need for solitude gets continually thwarted by the stress of competing demands on your time (or space), the result is an increase in feelings of aloneliness, which then increases stress and life dissatisfaction. This negative cycle can exacerbate internalizing symptoms (e.g. depression).
Know, that it's perfectly okay to want to be by yourself from time to time.