A sociable person may become withdrawn, a studious person cease going to class, they may sleep or eat a lot more or a lot less, might increase drug or alcohol use, become moody, sullen, or have a prolonged depression. They may bring you something of theirs you've admired and say they won't be needing it anymore, haphazardly give away things to people around them, or throw away things they have said were important. Suddenly This can take the form of going around telling people goodbye, suddenly talking about leaving but with no plans, making a will, writing letters to family and friends saying goodbye, or packing up their belongings.
Most people become depressed at some time.
It is always better to ask, than to ignore a depression. A Sudden Unexplained Lift in Spirits A person who has been depressed and showing other warning signs of suicide who suddently comes home looking happy and carefree, may be feeling the relief of finally making the decision of when and how to commit suicide.