Why was Douglass’s heart beating anxiously as the conductor approached him?

This heart-stopping episode comes from that fateful day when Frederick Douglass hopped aboard a train bound for New York in search of freedom. A previous attempt at breaking free from slavery two years before had failed, but Douglass remained undeterred; he would do whatever it took to gain his freedom.
On the day in question, Douglass has disguised himself as a free black sailor. It's a smart move, as there are lots of sailors in Baltimore, so he won't look out of place. The only problem is Douglass's identification papers. He borrowed them from a free seaman who doesn't bear any resemblance to him. If any railroad official examines those papers carefully, then Douglass's cover will be blown completely.
No wonder, then, that he's feeling so incredibly nervous when the conductor approaches him on board the train. Though trying ever so hard to stay calm on the outside, Douglass's heart is beating away like mad inside of him, as he knows that his whole future depends upon the conductor's decision. Thankfully, the conductor doesn't examine Douglass's documents too closely; instead, he quickly glances at the large, authoritative-looking American eagle at the top of the document before moving on his way.