Using present perfect continuous without mentioning time period

Solution 1:

When you use present perfect tense, the action you are describing is still happening (hence the label, present perfect). So, if you "have been looking forward to the holiday," you still are. And if you "have been sad," you still are.

(See English-At-Home for one reference.)

For further granularity, you might try

I had been feeling sad until I saw your smiling face just now.

or

I had been looking forward to the holiday, until I saw the weather forecast.

Solution 2:

In both of your sentences, I can still be looking forward to the holiday or feeling sad or no longer be looking forward to the holiday or feeling sad. So it can mean both in each case.

The most important thing to remember about this tense is that the present is affected by what was going on. For example, I might be explaining why I am very excited right now, or (in the second sentence) why my eyes are bloodshot and my face looks downcast right now.

Solution 3:

Mentioning a time period describes the beginning of the event, which persists until the present moment: "I have been looking forward to it today" indicates that during the day today I have been looking forward to it, and I still am.

The present perfect continuous will always include the current moment, even without other time indicators.

Regarding your specific questions:

"I have been looking forward to the holiday" does not specify whether it is currently the holiday or not. Either may be true.

"I have been feeling sad" always indicates that you still are. As soon as you are no longer sad, the sentence changes to "I had been feeling sad."