Tom,
If in doubt, get it checked out!
There may be a simple explanation as you have said yourself, perhaps you mistakenly give yourself to much insulin, mis-counted the carbs in your meal, or more booze than you remember. I am not sure about vomiting, but tiredness is a classic sign of a oncoming hypo in myself. I often feel tired and start yawning whilst going low, don't know why but I always check my blood glucose for reassurance when this happens. I just put it down to another crazy warning sign that comes with hypoglycemia.
Some time back there was a discussion on here about people having given themselves a insulin injection twice. It is surprising how many people have done this, and the consequences afterwards is fighting to normalise bg's, especially when you don't realise that you have given a double dose, and are at a lose to explain the situation. I know that you seem to be quite young, but I was talking with a elderly lady last year, and she had a horrendous time remember when she had injected herself. She would often forget to take her insulin but remember 1-2 hours later, or she would occasionally give the same dose twice. I felt really sorry for her predicament, and equally sorry for her husband too, whom she said dealt with the consequences of her forgetfulness.
Pleased you are OK now!
NIgel