Aloneness means being at peace with yourself, which implies that you are simply happy without any external influence. You are content with yourself and require no external validation. Rather your inner being is quiet and there is nothing troubling you. Hence, you simply are; doing whatever you want, not judging whether it is productive or unproductive, whether it will benefit you at a later stage or not. Aloneness is bliss. When you are Alone, mind is in your control.
Loneliness on the other hand is a painful state of mind wherein you feel incomplete, that something is missing and the mind is in turmoil. You need someone to talk to, or to go to someplace as you are experiencing the same things again and again. It is a feeling of saturation with the existing world- be it home or workplace. Loneliness leaves you facing the mind all alone and not finding anything to engage the mind. Hence, the mind takes over and starts subjecting you to its distortions. Loneliness is a feeling of not knowing what to do with your life, a general lack of purpose. You feel that time is simply ticking away and you are wasting it. During the periods of loneliness, one observes that time moves very, very slowly.
When someone is going through a phase of mental turmoil such as anxiety, depression etc, it is very difficult to be alone. In fact, Psychology says that in such conditions one should not be left to himself as these feelings will take over and aggravate the mental condition. It is advised that one should seek out people and stay connected to overcome the mental condition.
Each human being is unique and is born with some inherent talent. If he is able to find ways to express his talent, then work becomes play, otherwise work becomes a burden. The burden slowly starts taking its toll and leads to frustration which manifests itself as loneliness and depression. In order to overcome loneliness, it is extremely important to find ways and means to keep yourself engaged with things which you love to do and by which you are able to express yourself.
Man is born alone and dies alone. However, man is a social animal and needs society to express himself. According to Maslow, we have five categories of needs: physiological, safety, love, esteem, and self-actualization. In this theory, higher needs in the hierarchy emerge when people feel they have sufficiently satisfied the previous need. Man needs to progress through these needs sequentially and cannot jump directly to the top of the hierarchy. And missing one of the needs leads to a feeling of loneliness
Thus, one can say that while being alone is a bliss, being lonely is a curse which one would not like even his worst enemy to face.