Tramadol is an opioid. Under normal circumstances, physioloigcal symptoms of withdrawal are rather similar to the symptoms one gets with a mild flu. Malaise, lethargy, congestion, mild to moderate diarrhea (following constipation caused by the drug's effect of decreasing bowel motility) are all common. Withdrawal symptoms typically last around 2-4 days.
A note on misconceptions: unlike some drugs that have really severe withdrawal symptomology (ethanol and barbituates for instance), opiates and opioids -- contrary to the popular misconception --- yield a physiologically mild withdrawal that typically does not require treatment.
Note that psychological withdrawal (or more properly reversal of habituation), may yield a wider and longer lasting variety of psychosomatic and psychogentic symptoms, although this too is rare.