This is a little bit more difficult to write about since there's a variety of problems that make this very difficult to answer. First, PTSD is a relatively new concept starting with shell shock from the First World War; second, accounts are difficult at best to determine such things as diaries don't provide every detail needed to diagnosis PTSD but also because they're unreliable, the memoirs of Marshal MacDonald paint him in a better picture than reality, thus making it hard to be certain about anything, let alone show the bad things (such as PTSD symptoms); third, accounts are that frequent, while the Napoleonic Wars has a wealth of primary sources, they aren't very common among lower ranks than higher ranks, and the higher ranked accounts are memoirs meant to show off events rather than detail everything.

With that said, there is one person usually mentioned when discussing Napoleonic PTSD, Marshal Michel Ney. Ney is well known for his amazing rearguard actions in Spain and Russia, but he acts different afterward; he's aggressive and has mood changes, generally acting different than before. The largest evidence of his PTSD comes from his actions during the Hundred Days; he makes foolish attacks (more foolish than his normal command style) during the Battle of Quatre Bras and made foolish attacks that contributed heavily to the victory of the Allies at Waterloo. His cavalry charge on the British guns was without support and even at the guns, he was seen slapping the guns with the flat of his sword. At the end of the battle, when soldiers were retreating, he is known to have said "Come see how a Marshal of France dies" but was pulled back by a lower officer.

Another thing that must be noted before I can finish is the level of frequency that a soldier would experience battle. While we can look at the Napoleonic Wars as being a time of constant war and very silly fighting methods, a soldier wasn't under constant fire. Between battles, soldiers would march and make camp, guarding supply lines and establishing pickets. They wouldn't see the constant din of combat in the First World War, and there are even examples of soldiers talking to each other across picket lines, not fighting because they had little interest in fighting.

In all, it's very hard to say without a wider account of the lower ranks.